| 16 |
URL Rewriting for the Fearful |
I think it was Marilyn Monroe who said, “If you can’t handle me at my worst, please just fix these rewrite rules, I’m getting an internal server error.” Even the blonde bombshell hated configuring URL rewrites on her website, and I think most of us know where she was coming from.
The majority of website projects I work on require some amount of URL rewriting, and I find it mildly enjoyable — I quite like a good rewrite rule. I suspect you may not share my glee, so in this article we’re going to go back to basics to try to make the whole rigmarole more understandable.
When we think about URL rewriting, usually that means adding some rules to an .htaccess file for an Apache web server. As that’s the most common case, that’s what I’ll be sticking to here. If you work with a different server, there’s often documentation specifically for translating from Apache’s mod_rewrite rules. I even found an automatic converter for nginx.
This isn’t going to be a comprehensive guide to every URL rewriting problem you might ever have. That would take us until Christmas. If you consider yourself a trial-and-error dabbler in the HTTP 500-infested waters of URL rewriting, then hopefully this will provide a little bit more of a basis to help you figure out what you’re doing. If you’ve ever found yourself staring at the white screen of death after screwing up your .htaccess file, don’t worry. As Michael Jackson once insipidly whined, you are not alone.
The basics
Rewrite rules form part of the Apache web server’s configuration for a website, and can be placed in a number of different locations as part of your virtual host configuration. By far the simplest and most portable option is to use an .htaccess file in your website root. Provided your server has mod_rewrite available, all you need to do to kick things off in your .htaccess file is:
RewriteEngine on
The general formula for a rewrite rule is:
RewriteRule URL/to/match URL/to/use/if/it/matches [options]
When we talk about URL rewriting, we’re normally talking about one of two things: redirecting the browser to a different URL; or rewriting the URL internally to use a particular file. We’ll look at those in turn.
Redirects
Redirects match an incoming URL, and then redirect the user’s browser to a different address. These can be useful for maintaining legacy URLs if content changes location as part of a site redesign. Redirecting the old URL to the new location makes sure that any incoming links, such as those from search engines, continue to work.
In 1998, Sir Tim Berners-Lee wrote that Cool URIs don’t change, encouraging us all to go the extra mile to make sure links keep working forever. I think that sometimes it’s fine to move things around — especially to correct bad URL design choices of the past — provided that you can do so while keeping those old URLs working. That’s where redirects can help.
A redirect might look like this
RewriteRule ^article/used/to/be/here.php$ /article/now/lives/here/ [R=301,L]
Rewriting
By default, web servers closely map page URLs to the files in your site. On receiving a request for http://example.com/about/history.html the server goes to the configured folder for the example.com website, and then goes into the about folder and returns the history.html file.
A rewrite rule changes that process by breaking the direct relationship between the URL and the file system. “When there’s a request for /about/history.html” a rewrite rule might say, “use the file /about_section.php instead.”
This opens up lots of possibilities for creative ways to map URLs to the files that know how to serve up the page. Most MVC frameworks will have a single rule to rewrite all page URLs to one single file. That file will be a script which kicks off the framework to figure out what to do to serve the page.
RewriteRule ^for/this/url/$ /use/this/file.php [L]
Matching patterns
By now you’ll have noted the weird ^ and $ characters wrapped around the URL we’re trying to match. That’s because what we’re actually using here is a pattern. Technically, it is what’s called a Perl Compatible Regular Expression (PCRE) or simply a regex or regexp. We’ll call it a pattern because we’re not animals.
What are these patterns? If I asked you to enter your credit card expiry date as MM/YY then chances are you’d wonder what I wanted your credit card details for, but you’d know that I wanted a two-digit month, a slash, and a two-digit year. That’s not a regular expression, but it’s the same idea: using some placeholder characters to define the pattern of the input you’re trying to match.
We’ve already met two regexp characters.
^
Matches the beginning of a string
$
Matches the end of a string
When a pattern starts with ^ and ends with $ it’s to make sure we match the complete URL start to finish, not just part of it. There are lots of other ways to match, too:
[0-9]
Matches a number, 0–9. [2-4] would match numbers 2 to 4 inclusive.
[a-z]
Matches lowercase letters a–z
[A-Z]
Matches uppercase letters A–Z
[a-z0-9]
Combining some of these, this matches letters a–z and numbers 0–9
These are what we call character groups. The square brackets basically tell the server to match from the selection of characters within them. You can put any specific characters you’re looking for within the brackets, as well as the ranges shown above.
However, all these just match one single character. [0-9] would match 8 but not 84 — to match 84 we’d need to use [0-9] twice.
[0-9][0-9]
So, if we wanted to match 1984 we could to do this:
[0-9][0-9][0-9][0-9]
…but that’s getting silly. Instead, we can do this:
[0-9]{4}
That means any character between 0 and 9, four times. If we wanted to match a number, but didn’t know how long it might be (for example, a database ID in the URL) we could use the + symbol, which means one or more.
[0-9]+
This now matches 1, 123 and 1234567.
Putting it into practice
Let’s say we need to write a rule to match article URLs for this website, and to rewrite them to use /article.php under the hood. The articles all have URLs like this:
2013/article-title/
They start with a year (from 2005 up to 2013, currently), a slash, and then have a URL-safe version of the article title (a slug), ending in a slash. We’d match it like this:
^[0-9]{4}/[a-z0-9-]+/$
If that looks frightening, don’t worry. Breaking it down, from the start of the URL (^) we’re looking for four numbers ([0-9]{4}). Then a slash — that’s just literal — and then anything lowercase a–z or 0–9 or a dash ([a-z0-9-]) one or more times (+), ending in a slash (/$).
Putting that into a rewrite rule, we end up with this:
RewriteRule ^[0-9]{4}/[a-z0-9-]+/$ /article.php
We’re getting close now. We can match the article URLs and rewrite them to use article.php. Now we just need to make sure that article.php knows which article it’s supposed to display.
Capturing groups, and replacements
When rewriting URLs you’ll often want to take important parts of the URL you’re matching and pass them along to the script that handles the request. That’s usually done by adding those parts of the URL on as query string arguments. For our example, we want to make sure that article.php knows the year and the article title we’re looking for. That means we need to call it like this:
/article.php?year=2013&slug=article-title
To do this, we need to mark which parts of the pattern we want to reuse in the destination. We do this with round brackets or parentheses. By placing parentheses around parts of the pattern we want to reuse, we create what’s called a capturing group. To capture an important part of the source URL to use in the destination, surround it in parentheses.
Our pattern now looks like this, with parentheses around the parts that match the year and slug, but ignoring the slashes:
^([0-9]{4})/([a-z0-9-]+)/$
To use the capturing groups in the destination URL, we use the dollar sign and the number of the group we want to use. So, the first capturing group is $1, the second is $2 and so on. (The $ is unrelated to the end-of-pattern $ we used before.)
RewriteRule ^([0-9]{4})/([a-z0-9-]+)/$ /article.php?year=$1&slug=$2
The value of the year capturing group gets used as $1 and the article title slug is $2. Had there been a third group, that would be $3 and so on. In regexp parlance, these are called back-references as they refer back to the pattern.
Options
Several brain-taxing minutes ago, I mentioned some options as the final part of a rewrite rule. There are lots of options (or flags) you can set to change how the rule is processed. The most useful (to my mind) are:
R=301
Perform an HTTP 301 redirect to send the user’s browser to the new URL. A status of 301 means a resource has moved permanently and so it’s a good way of both redirecting the user to the new URL, and letting search engines know to update their indexes.
L
Last. If this rule matches, don’t bother processing the following rules.
Options are set in square brackets at the end of the rule. You can set multiple options by separating them with commas:
RewriteRule ^([0-9]{4})/([a-z0-9-]+)/$ /article.php?year=$1&slug=$2 [L]
or
RewriteRule ^about/([a-z0-9-]+).jsp/$ /about/$1/ [R=301,L]
Common pitfalls
Once you’ve built up a few rewrite rules, things can start to go wrong. You may have been there: a rule which looks perfectly good is somehow not matching. One common reason for this is hidden behind that [L] flag.
L for Last is a useful option to tell the rewrite engine to stop once the rule has been matched. This is what it does — the remaining rules in the .htaccess file are then ignored. However, once a URL has been rewritten, the entire set of rules are then run again on the new URL. If the new URL matches any of the rules, that too will be rewritten and on it goes.
One way to avoid this problem is to keep your ‘real’ pages under a folder path that will never match one of your rules, or that you can exclude from the rewrite rules.
Useful snippets
I find myself reusing the same few rules over and over again, just with minor changes. Here are some useful examples to refer back to.
Excluding a directory
As mentioned above, if you’re rewriting lots of fancy URLs to a collection of real files it can be helpful to put those files in a folder and exclude it from rewrite rules. This helps solve the issue of rewrite rules reapplying to your newly rewritten URL. To exclude a directory, put a rule like this at the top of your file, before your other rules. Our files are in a folder called _source, the dash in the rule means do nothing, and the L flag means the following rules won’t be applied.
RewriteRule ^_source - [L]
This is also useful for excluding things like CMS folders from your website’s rewrite rules
RewriteRule ^perch - [L]
Adding or removing www from the domain
Some folk like to use a www and others don’t. Usually, it’s best to pick one and go with it, and redirect the one you don’t want. On this site, we don’t use www.24ways.org so we redirect those requests to 24ways.org.
This uses a RewriteCond which is like an if for a rewrite rule: “If this condition matches, then apply the following rule.” In this case, it’s if the HTTP HOST (or domain name, basically) matches this pattern, then redirect everything:
RewriteCond %{HTTP_HOST} ^www.24ways.org$ [NC]
RewriteRule ^(.*)$ http://24ways.org/$1 [R=301,L]
The [NC] flag means ‘no case’ — the match is case-insensitive. The dots in the domain are escaped with a backslash, as a dot is a regular expression character which means match anything, so we escape it because we literally mean a dot in this instance.
Removing file extensions
Sometimes all you need to do to tidy up a URL is strip off the technology-specific file extension, so that /about/history.php becomes /about/history. This is easily achieved with the help of some more rewrite conditions.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule ^(.+)$ $1.php [L,QSA]
This says if the file being asked for isn’t a file (!-f) and if it isn’t a directory (!-d) and if the file name plus .php is an actual file (-f) then rewrite by adding .php on the end. The QSA flag means ‘query string append’: append the existing query string onto the rewritten URL.
It’s these sorts of more generic catch-all rules that you need to watch out for when your .htaccess gets rerun after a successful match. Without care they can easily rematch the newly rewritten URL.
Logging for when it all goes wrong
Although not possible within your .htaccess file, if you have access to your Apache configuration files you can enable rewrite logging. This can be useful to track down where a rule is going wrong, if it’s matching incorrectly or failing to match. It also gives you an overview of the amount of work being done by the rewrite engine, enabling you to rearrange your rules and maximise performance.
RewriteEngine On
RewriteLog "/full/system/path/to/rewrite.log"
RewriteLogLevel 5
To be doubly clear: this will not work from an .htaccess file — it needs to be added to the main Apache configuration files. (I sometimes work using MAMP PRO locally on my Mac, and this can be pasted into the snappily named Customized virtual host general settings box in the Advanced tab for your site.)
The white screen of death
One of the most frustrating things when working with rewrite rules is that when you make a mistake it can result in the server returning an HTTP 500 Internal Server Error. This in itself isn’t an error message, of course. It’s more of a notification that an error has occurred. The real error message can usually be found in your Apache error log.
If you have access to your server logs, check the Apache error log and you’ll usually find a much more descriptive error message, pointing you towards your mistake. (Again, if using MAMP PRO, go to Server, Apache and the View Log button.)
In conclusion
Rewriting URLs can be a bear, but the advantages are clear. Keeping a tidy URL structure, disconnected from the technology or file structure of your site can result in URLs that are easier to use and easier to maintain into the future.
If you’re redesigning a site, remember that cool URIs don’t change, so budget some time to make sure that any content you move has a rewrite rule associated with it to keep any links working.
Further reading
To find out more about URL rewriting and perhaps even learn more about regular expressions, I can recommend the following resources.
From the horse’s mouth, the Apache mod_rewrite documentation
Particularly useful with that documentation is the RewriteRule Flags listing
You may wish to don sunglasses to follow the otherwise comprehensive Regular-Expressions.info tutorial
Friend of 24 ways, Neil Crosby has a mod_rewrite Beginner’s Guide which I’ve found handy over the years.
As noted at the start, this isn’t a fully comprehensive guide, but I hope it’s useful in finding your feet with a powerful but sometimes annoying technology. Do you have useful snippets you often use on projects? Feel free to share them in the comments. |
2013 |
Drew McLellan |
drewmclellan |
2013-12-01T00:00:00+00:00 |
https://24ways.org/2013/url-rewriting-for-the-fearful/ |
code |
| 80 |
HTML5 Video Bumpers |
Video is a bigger part of the web experience than ever before. With native browser support for HTML5 video elements freeing us from the tyranny of plugins, and the availability of faster internet connections to the workplace, home and mobile networks, it’s now pretty straightforward to publish video in a way that can be consumed in all sorts of ways on all sorts of different web devices.
I recently worked on a project where the client had shot some dedicated video shorts to publish on their site. They also had some five-second motion graphics produced to top and tail the videos with context and branding. This pretty common requirement is a great idea on the web, where a user might land at your video having followed a link and be viewing a page without much context.
Known as bumpers, these short introduction clips help brand a video and make it look a lot more professional.
Adding bumpers to a video
The simplest way to add bumpers to a video would be to edit them on to the start and end of the video file itself. Cooking the bumpers into the video file is easy, but should you ever want to update them it can become a real headache. If the branding needs updating, for example, you’d need to re-edit and re-encode all your videos. Not a fun task.
What if the bumpers could be added dynamically? That would enable you to use the same bumper for multiple videos (decreasing download time for users who might watch more than one) and to update the bumpers whenever you wanted. You could change them seasonally, update them for special promotions, run different advertising slots, perform multivariate testing, or even target different bumpers to different users.
The trade-off, of course, is that if you dynamically add your bumpers, there’s a chance that a user in a given circumstance might not see the bumper. For example, if the main video feature was uploaded to YouTube, you’d have no way to control the playback. As always, you need to weigh up the pros and cons and make your choice.
HTML5 bumpers
If you wanted to dynamically add bumpers to your HTML5 video, how would you go about it? That was the question I found myself needing to answer for this particular client project.
My initial thought was to treat it just like an image slideshow. If I were building a slideshow that moved between images, I’d use CSS absolute positioning with z-index to stack the images up on top of each other in a pile, with the first image on top. To transition to the second image, I’d use JavaScript to fade the top image out, revealing the second image beneath it.
Now that video is just a native object in the DOM, just like an image, why not do the same? Stack the videos up with the opening bumper on top, listen for the video’s onended event, and fade it out to reveal the main feature behind. Good idea, right?
Wrong
Remember that this is the web. It’s never going to be that easy. The problem here is that many non-desktop devices use native, dedicated video players. Think about watching a video on a mobile phone – when you play the video, the phone often goes full-screen in its native player, leaving the web page behind. There’s no opportunity to fade or switch z-index, as the video isn’t being viewed in the page. Your page is left powerless. Powerless!
So what can we do? What can we control?
Those of us with particularly long memories might recall a time before CSS, when we’d have to use JavaScript to perform image rollovers. As CSS background images weren’t a practical reality, we would use lots of <img> elements, and perform a rollover by modifying the src attribute of the image.
Turns out, this old trick of modifying the source can help us out with video, too. In most cases, modifying the src attribute of a <video> element, or perhaps more likely the src attribute of a source element, will swap from one video to another.
Swappin’ it
Let’s take a deliberately simple example of a super-basic video tag:
<video src="mycat.webm" controls>no fallback coz i is lame, innit.</video>
We could very simply write a script to find all video tags and give them a new src to show our bumper.
<script>
var videos, i, l;
videos = document.getElementsByTagName('video');
for(i=0, l=videos.length; i<l; i++) {
videos[i].setAttribute('src', 'bumper-in.webm');
}
</script>
View the example in a browser with WebM support. You’ll see that the video is swapped out for the opening bumper. Great!
Beefing it up
Of course, we can’t just publish video in one format. In practical use, you need a <video> element with multiple <source> elements containing your different source formats.
<video controls>
<source src="mycat.mp4" type="video/mp4" />
<source src="mycat.webm" type="video/webm" />
<source src="mycat.ogv" type="video/ogg" />
</video>
This time, our script needs to loop through the sources, not the videos. We’ll use a regular expression replacement to swap out the file name while maintaining the correct file extension.
<script>
var sources, i, l, orig;
sources = document.getElementsByTagName('source');
for(i=0, l=sources.length; i<l; i++) {
orig = sources[i].getAttribute('src');
sources[i].setAttribute('src', orig.replace(/(w+).(w+)/, 'bumper-in.$2'));
// reload the video
sources[i].parentNode.load();
}
</script>
The difference this time is that when changing the src of a <source> we need to call the .load() method on the video to get it to acknowledge the change.
See the code in action, this time in a wider range of browsers.
But, my video!
I guess we should get the original video playing again. Keeping the same markup, we need to modify the script to do two things:
Store the original src in a data- attribute so we can access it later
Add an event listener so we can detect the end of the bumper playing, and load the original video back in
As we need to loop through the videos this time to add the event listener, I’ve moved the .load() call into that loop. It’s a bit more efficient to call it only once after modifying all the video’s sources.
<script>
var videos, sources, i, l, orig;
sources = document.getElementsByTagName('source');
for(i=0, l=sources.length; i<l; i++) {
orig = sources[i].getAttribute('src');
sources[i].setAttribute('data-orig', orig);
sources[i].setAttribute('src', orig.replace(/(w+).(w+)/, 'bumper-in.$2'));
}
videos = document.getElementsByTagName('video');
for(i=0, l=videos.length; i<l; i++) {
videos[i].load();
videos[i].addEventListener('ended', function(){
sources = this.getElementsByTagName('source');
for(i=0, l=sources.length; i<l; i++) {
orig = sources[i].getAttribute('data-orig');
if (orig) {
sources[i].setAttribute('src', orig);
}
sources[i].setAttribute('data-orig','');
}
this.load();
this.play();
});
}
</script>
Again, view the example to see the bumper play, followed by our spectacular main feature. (That’s my cat, Widget. His interests include sleeping and internet marketing.)
Tidying things up
The final thing to do is add our closing bumper after the main video has played. This involves the following changes:
We need to keep track of whether the src has been changed, so we only play the video if it’s changed. I’ve added the modified variable to track this, and it stops us getting into a situation where the video just loops forever.
Add an else to the event listener, for when the orig is false (so the main feature has been playing) to load in the end bumper. We also check that we’re not already playing the end bumper. Because looping.
<script>
var videos, sources, i, l, orig, current, modified;
sources = document.getElementsByTagName('source');
for(i=0, l=sources.length; i<l; i++) {
orig = sources[i].getAttribute('src');
sources[i].setAttribute('data-orig', orig);
sources[i].setAttribute('src', orig.replace(/(w+).(w+)/, 'bumper-in.$2'));
}
videos = document.getElementsByTagName('video');
for(i=0, l=videos.length; i<l; i++) {
videos[i].load();
modified = false;
videos[i].addEventListener('ended', function(){
sources = this.getElementsByTagName('source');
for(i=0, l=sources.length; i<l; i++) {
orig = sources[i].getAttribute('data-orig');
if (orig) {
sources[i].setAttribute('src', orig);
modified = true;
}else{
current = sources[i].getAttribute('src');
if (current.indexOf('bumper-out')==-1) {
sources[i].setAttribute('src', current.replace(/([w]+).(w+)/, 'bumper-out.$2'));
modified = true;
}else{
this.pause();
modified = false;
}
}
sources[i].setAttribute('data-orig','');
}
if (modified) {
this.load();
this.play();
}
});
}
</script>
Yo ho ho, that’s a lot of JavaScript. See it in action – you should get a bumper, the cat video, and an end bumper.
Of course, this code works fine for demonstrating the principle, but it’s very procedural. Nothing wrong with that, but to do something similar in production, you’d probably want to make the code more modular to ease maintainability. Besides, you may want to use a framework, rather than basic JavaScript.
The end credits
One really important principle here is that of progressive enhancement. If the browser doesn’t support JavaScript, the user won’t see your bumper, but they will get the main video. If the browser supports JavaScript but doesn’t allow you to modify the src (as was the case with older versions of iOS), the user won’t see your bumper, but they will get the main video.
If a search engine or social media bot grabs your page and looks for content, they won’t see your bumper, but they will get the main video – which is absolutely what you want.
This means that if the bumper is absolutely crucial, you may still need to cook it into the video. However, for many applications, running it dynamically can work quite well.
As always, it comes down to three things:
Measure your audience: know how people access your site
Test the solution: make sure it works for your audience
Plan for failure: it’s the web and that’s how things work ‘round these parts
But most of all play around with it, have fun and build something awesome. |
2012 |
Drew McLellan |
drewmclellan |
2012-12-01T00:00:00+00:00 |
https://24ways.org/2012/html5-video-bumpers/ |
code |
| 124 |
Writing Responsible JavaScript |
Without a doubt, JavaScript has been making something of a comeback in the last year. If you’re involved in client-side development in any way at all, chances are that you’re finding yourself writing more JavaScript now than you have in a long time.
If you learned most of your JavaScript back when DHTML was all the rage and before DOM Scripting was in vogue, there have been some big shifts in the way scripts are written. Most of these are in the way event handlers are assigned and functions declared. Both of these changes are driven by the desire to write scripts that are responsible page citizens, both in not tying behaviour to content and in taking care not to conflict with other scripts. I thought it may be useful to look at some of these more responsible approaches to learn how to best write scripts that are independent of the page content and are safely portable between different applications.
Event Handling
Back in the heady days of Web 1.0, if you wanted to have an object on the page react to something like a click, you would simply go ahead and attach an onclick attribute. This was easy and understandable, but much like the font tag or the style attribute, it has the downside of mixing behaviour or presentation in with our content. As we’re learned with CSS, there are big benefits in keeping those layers separate. Hey, if it works for CSS, it should work for JavaScript too.
Just like with CSS, instead of adding an attribute to our element within the document, the more responsible way to do that is to look for the item from your script (like CSS does with a selector) and then assign the behaviour to it. To give an example, take this oldskool onclick use case:
<a id="anim-link" href="#" onclick="playAnimation()">Play the animation</a>
This could be rewritten by removing the onclick attribute, and instead doing the following from within your JavaScript.
document.getElementById('anim-link').onclick = playAnimation;
It’s all in the timing
Of course, it’s never quite that easy. To be able to attach that onclick, the element you’re targeting has to exist in the page, and the page has to have finished loading for the DOM to be available. This is where the onload event is handy, as it fires once everything has finished loading. Common practise is to have a function called something like init() (short for initialise) that sets up all these event handlers as soon as the page is ready.
Back in the day we would have used the onload attibute on the <body> element to do this, but of course what we really want is:
window.onload = init;
As an interesting side note, we’re using init here rather than init() so that the function is assigned to the event. If we used the parentheses, the init function would have been run at that moment, and the result of running the function (rather than the function itself) would be assigned to the event. Subtle, but important.
As is becoming apparent, nothing is ever simple, and we can’t just go around assigning our initialisation function to window.onload. What if we’re using other scripts in the page that might also want to listen out for that event? Whichever script got there last would overwrite everything that came before it. To manage this, we need a script that checks for any existing event handlers, and adds the new handler to it. Most of the JavaScript libraries have their own systems for doing this. If you’re not using a library, Simon Willison has a good stand-alone example
function addLoadEvent(func) {
var oldonload = window.onload;
if (typeof window.onload != 'function') {
window.onload = func;
} else {
window.onload = function() {
if (oldonload) {
oldonload();
}
func();
}
}
}
Obviously this is just a toe in the events model’s complex waters. Some good further reading is PPK’s Introduction to Events.
Carving out your own space
Another problem that rears its ugly head when combining multiple scripts on a single page is that of making sure that the scripts don’t conflict. One big part of that is ensuring that no two scripts are trying to create functions or variables with the same names. Reusing a name in JavaScript just over-writes whatever was there before it.
When you create a function in JavaScript, you’ll be familiar with doing something like this.
function foo() {
... goodness ...
}
This is actually just creating a variable called foo and assigning a function to it. It’s essentially the same as the following.
var foo = function() {
... goodness ...
}
This name foo is by default created in what’s known as the ‘global namespace’ – the general pool of variables within the page. You can quickly see that if two scripts use foo as a name, they will conflict because they’re both creating those variables in the global namespace.
A good solution to this problem is to add just one name into the global namespace, make that one item either a function or an object, and then add everything else you need inside that. This takes advantage of JavaScript’s variable scoping to contain you mess and stop it interfering with anyone else.
Creating An Object
Say I was wanting to write a bunch of functions specifically for using on a site called ‘Foo Online’. I’d want to create my own object with a name I think is likely to be unique to me.
var FOOONLINE = {};
We can then start assigning functions are variables to it like so:
FOOONLINE.message = 'Merry Christmas!';
FOOONLINE.showMessage = function() {
alert(this.message);
};
Calling FOOONLINE.showMessage() in this example would alert out our seasonal greeting. The exact same thing could also be expressed in the following way, using the object literal syntax.
var FOOONLINE = {
message: 'Merry Christmas!',
showMessage: function() {
alert(this.message);
}
};
Creating A Function to Create An Object
We can extend this idea bit further by using a function that we run in place to return an object. The end result is the same, but this time we can use closures to give us something like private methods and properties of our object.
var FOOONLINE = function(){
var message = 'Merry Christmas!';
return {
showMessage: function(){
alert(message);
}
}
}();
There are two important things to note here. The first is the parentheses at the end of line 10. Just as we saw earlier, this runs the function in place and causes its result to be assigned. In this case the result of our function is the object that is returned at line 4.
The second important thing to note is the use of the var keyword on line 2. This ensures that the message variable is created inside the scope of the function and not in the global namespace. Because of the way closure works (which if you’re not familiar with, just suspend your disbelief for a moment) that message variable is visible to everything inside the function but not outside. Trying to read FOOONLINE.message from the page would return undefined.
This is useful for simulating the concept of private class methods and properties that exist in other programming languages. I like to take the approach of making everything private unless I know it’s going to be needed from outside, as it makes the interface into your code a lot clearer for someone else to read.
All Change, Please
So that was just a whistle-stop tour of a couple of the bigger changes that can help to make your scripts better page citizens. I hope it makes useful Sunday reading, but obviously this is only the tip of the iceberg when it comes to designing modular, reusable code.
For some, this is all familiar ground already. If that’s the case, I encourage you to perhaps submit a comment with any useful resources you’ve found that might help others get up to speed. Ultimately it’s in all of our interests to make sure that all our JavaScript interoperates well – share your tips. |
2006 |
Drew McLellan |
drewmclellan |
2006-12-10T00:00:00+00:00 |
https://24ways.org/2006/writing-responsible-javascript/ |
code |
| 132 |
Tasty Text Trimmer |
In most cases, when designing a user interface it’s best to make a decision about how data is best displayed and stick with it. Failing to make a decision ultimately leads to too many user options, which in turn can be taxing on the poor old user.
Under some circumstances, however, it’s good to give the user freedom in customising their workspace. One good example of this is the ‘Article Length’ tool in Apple’s Safari RSS reader. Sliding a slider left of right dynamically changes the length of each article shown. It’s that kind of awesomey magic stuff that’s enough to keep you from sleeping. Let’s build one.
The Setup
Let’s take a page that has lots of long text items, a bit like a news page or like Safari’s RSS items view. If we were to attach a class name to each element we wanted to resize, that would give us something to hook onto from the JavaScript.
Example 1: The basic page.
As you can see, I’ve wrapped my items in a DIV and added a class name of chunk to them. It’s these chunks that we’ll be finding with the JavaScript. Speaking of which …
Our Core Functions
There are two main tasks that need performing in our script. The first is to find the chunks we’re going to be resizing and store their original contents away somewhere safe. We’ll need this so that if we trim the text down we’ll know what it was if the user decides they want it back again. We’ll call this loadChunks.
var loadChunks = function(){
var everything = document.getElementsByTagName('*');
var i, l;
chunks = [];
for (i=0, l=everything.length; i<l; i++){
if (everything[i].className.indexOf(chunkClass) > -1){
chunks.push({
ref: everything[i],
original: everything[i].innerHTML
});
}
}
};
The variable chunks is stored outside of this function so that we can access it from our next core function, which is doTrim.
var doTrim = function(interval) {
if (!chunks) loadChunks();
var i, l;
for (i=0, l=chunks.length; i<l; i++){
var a = chunks[i].original.split(' ');
a = a.slice(0, interval);
chunks[i].ref.innerHTML = a.join(' ');
}
};
The first thing that needs to be done is to call loadChunks if the chunks variable isn’t set. This should only happen the first time doTrim is called, as from that point the chunks will be loaded.
Then all we do is loop through the chunks and trim them. The trimming itself (lines 6-8) is very simple. We split the text into an array of words (line 6), then select only a portion from the beginning of the array up until the number we want (line 7). Finally the words are glued back together (line 8).
In essense, that’s it, but it leaves us needing to know how to get the number into this function in the first place, and how that number is generated by the user. Let’s look at the latter case first.
The YUI Slider Widget
There are lots of JavaScript libraries available at the moment. A fair few of those are really good. I use the Yahoo! User Interface Library professionally, but have only recently played with their pre-build slider widget. Turns out, it’s pretty good and perfect for this task.
Once you have the library files linked in (check the docs linked above) it’s fairly straightforward to create yourself a slider.
slider = YAHOO.widget.Slider.getHorizSlider("sliderbg", "sliderthumb", 0, 100, 5);
slider.setValue(50);
slider.subscribe("change", doTrim);
All that’s needed then is some CSS to make the slider look like a slider, and of course a few bits of HTML. We’ll see those later.
See It Working!
Rather than spell out all the nuts and bolts of implementing this fairly simple script, let’s just look at in it action and then pick on some interesting bits I’ve added.
Example 2: Try the Tasty Text Trimmer.
At the top of the JavaScript file I’ve added a small number of settings.
var chunkClass = 'chunk';
var minValue = 10;
var maxValue = 100;
var multiplier = 5;
Obvious candidates for configuration are the class name used to find the chunks, and also the some minimum and maximum values. The minValue is the fewest number of words we wish to display when the slider is all the way down. The maxValue is the length of the slider, in this case 100.
Moving the slider makes a call to our doTrim function with the current value of the slider. For a slider 100 pixels long, this is going to be in the range of 0-100. That might be okay for some things, but for longer items of text you’ll want to allow for displaying more than 100 words. I’ve accounted for this by adding in a multiplier – in my code I’m multiplying the value by 5, so a slider value of 50 shows 250 words. You’ll probably want to tailor the multiplier to the type of content you’re using.
Keeping it Accessible
This effect isn’t something we can really achieve without JavaScript, but even so we must make sure that this functionality has no adverse impact on the page when JavaScript isn’t available. This is achieved by adding the slider markup to the page from within the insertSliderHTML function.
var insertSliderHTML = function(){
var s = '<a id="slider-less" href="#less"><img src="icon_min.gif" width="10" height="10" alt="Less text" class="first" /></a>';
s +=' <div id="sliderbg"><div id="sliderthumb"><img src="sliderthumbimg.gif" /></div></div>';
s +=' <a id="slider-more" href="#more"><img src="icon_max.gif" width="10" height="10" alt="More text" /></a>';
document.getElementById('slider').innerHTML = s;
}
The other important factor to consider is that a slider can be tricky to use unless you have good eyesight and pretty well controlled motor skills. Therefore we should provide a method of changing the value by the keyboard.
I’ve done this by making the icons at either end of the slider links so they can be tabbed to. Clicking on either icon fires the appropriate JavaScript function to show more or less of the text.
In Conclusion
The upshot of all this is that without JavaScript the page just shows all the text as it normally would. With JavaScript we have a slider for trimming the text excepts that can be controlled with the mouse or with a keyboard.
If you’re like me and have just scrolled to the bottom to find the working demo, here it is again:
Try the Tasty Text Trimmer
Trimmer for Christmas? Don’t say I never give you anything! |
2006 |
Drew McLellan |
drewmclellan |
2006-12-01T00:00:00+00:00 |
https://24ways.org/2006/tasty-text-trimmer/ |
code |
| 165 |
Transparent PNGs in Internet Explorer 6 |
Newer breeds of browser such as Firefox and Safari have offered support for PNG images with full alpha channel transparency for a few years. With the use of hacks, support has been available in Internet Explorer 5.5 and 6, but the hacks are non-ideal and have been tricky to use. With IE7 winning masses of users from earlier versions over the last year, full PNG alpha-channel transparency is becoming more of a reality for day-to-day use.
However, there are still numbers of IE6 users out there who we can’t leave out in the cold this Christmas, so in this article I’m going to look what we can do to support IE6 users whilst taking full advantage of transparency for the majority of a site’s visitors.
So what’s alpha channel transparency?
Cast your minds back to the Ghost of Christmas Past, the humble GIF. Images in GIF format offer transparency, but that transparency is either on or off for any given pixel. Each pixel’s either fully transparent, or a solid colour. In GIF, transparency is effectively just a special colour you can chose for a pixel.
The PNG format tackles the problem rather differently. As well as having any colour you chose, each pixel also carries a separate channel of information detailing how transparent it is. This alpha channel enables a pixel to be fully transparent, fully opaque, or critically, any step in between.
This enables designers to produce images that can have, for example, soft edges without any of the ‘halo effect’ traditionally associated with GIF transparency. If you’ve ever worked on a site that has different colour schemes and therefore requires multiple versions of each graphic against a different colour, you’ll immediately see the benefit.
What’s perhaps more interesting than that, however, is the extra creative freedom this gives designers in creating beautiful sites that can remain web-like in their ability to adjust, scale and reflow.
The Internet Explorer problem
Up until IE7, there has been no fully native support for PNG alpha channel transparency in Internet Explorer. However, since IE5.5 there has been some support in the form of proprietary filter called the AlphaImageLoader. Internet Explorer filters can be applied directly in your CSS (for both inline and background images), or by setting the same CSS property with JavaScript.
CSS:
img {
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(...);
}
JavaScript:
img.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(...)";
That may sound like a problem solved, but all is not as it may appear. Firstly, as you may realise, there’s no CSS property called filter in the W3C CSS spec. It’s a proprietary extension added by Microsoft that could potentially cause other browsers to reject your entire CSS rule.
Secondly, AlphaImageLoader does not magically add full PNG transparency support so that a PNG in the page will just start working. Instead, when applied to an element in the page, it draws a new rendering surface in the same space that element occupies and loads a PNG into it. If that sounds weird, it’s because that’s precisely what it is. However, by and large the result is that PNGs with an alpha channel can be accommodated.
The pitfalls
So, whilst support for PNG transparency in IE5.5 and 6 is possible, it’s not without its problems.
Background images cannot be positioned or repeated
The AlphaImageLoader does work for background images, but only for the simplest of cases. If your design requires the image to be tiled (background-repeat) or positioned (background-position) you’re out of luck. The AlphaImageLoader allows you to set a sizingMethod to either crop the image (if necessary) or to scale it to fit. Not massively useful, but something at least.
Delayed loading and resource use
The AlphaImageLoader can be quite slow to load, and appears to consume more resources than a standard image when applied. Typically, you’d need to add thousands of GIFs or JPEGs to a page before you saw any noticeable impact on the browser, but with the AlphaImageLoader filter applied Internet Explorer can become sluggish after just a handful of alpha channel PNGs.
The other noticeable effect is that as more instances of the AlphaImageLoader are applied, the longer it takes to render the PNGs with their transparency. The user sees the PNG load in its original non-supported state (with black or grey areas where transparency should be) before one by one the filter kicks in and makes them properly transparent.
Both the issue of sluggish behaviour and delayed load only really manifest themselves with volume and size of image. Use just a couple of instances and it’s fine, but be careful adding more than five or six. As ever, test, test, test.
Links become unclickable, forms unfocusable
This is a big one. There’s a bug/weirdness with AlphaImageLoader that sometimes prevents interaction with links and forms when a PNG background image is used. This is sometimes reported as a z-index issue, but I don’t believe it is. Rather, it’s an artefact of that weird way the filter gets applied to the document almost outside of the normal render process.
Often this can be solved by giving the links or form elements hasLayout using position: relative; where possible. However, this doesn’t always work and the non-interaction problem cannot always be solved. You may find yourself having to go back to the drawing board.
Sidestepping the danger zones
Frankly, it’s pretty bad news if you design a site, have that design signed off by your client, build it and then find out only at the end (because you don’t know what might trigger a problem) that your search field can’t be focused in IE6. That’s an absolute nightmare, and whilst it’s not likely to happen, it’s possible that it might. It’s happened to me. So what can you do?
The best approach I’ve found to this scenario is
Isolate the PNG or PNGs that are causing the problem. Step through the PNGs in your page, commenting them out one by one and retesting. Typically it’ll be the nearest PNG to the problem, so try there first. Keep going until you can click your links or focus your form fields.
This is where you really need luck on your side, because you’re going to have to fake it. This will depend on the design of the site, but some way or other create a replacement GIF or JPEG image that will give you an acceptable result. Then use conditional comments to serve that image to only users of IE older than version 7.
A hack, you say? Well, you started it chum.
Applying AlphaImageLoader
Because the filter property is invalid CSS, the safest pragmatic approach is to apply it selectively with JavaScript for only Internet Explorer versions 5.5 and 6. This helps ensure that by default you’re serving standard CSS to browsers that support both the CSS and PNG standards correct, and then selectively patching up only the browsers that need it.
Several years ago, Aaron Boodman wrote and released a script called sleight for doing just that. However, sleight dealt only with images in the page, and not background images applied with CSS. Building on top of Aaron’s work, I hacked sleight and came up with bgsleight for applying the filter to background images instead. That was in 2003, and over the years I’ve made a couple of improvements here and there to keep it ticking over and to resolve conflicts between sleight and bgsleight when used together. However, with alpha channel PNGs becoming much more widespread, it’s time for a new version.
Introducing SuperSleight
SuperSleight adds a number of new and useful features that have come from the day-to-day needs of working with PNGs.
Works with both inline and background images, replacing the need for both sleight and bgsleight
Will automatically apply position: relative to links and form fields if they don’t already have position set. (Can be disabled.)
Can be run on the entire document, or just a selected part where you know the PNGs are. This is better for performance.
Detects background images set to no-repeat and sets the scaleMode to crop rather than scale.
Can be re-applied by any other JavaScript in the page – useful if new content has been loaded by an Ajax request.
Download SuperSleight
Implementation
Getting SuperSleight running on a page is quite straightforward, you just need to link the supplied JavaScript file (or the minified version if you prefer) into your document inside conditional comments so that it is delivered to only Internet Explorer 6 or older.
<!--[if lte IE 6]>
<script type="text/javascript" src="supersleight-min.js"></script>
<![endif]-->
Supplied with the JavaScript is a simple transparent GIF file. The script replaces the existing PNG with this before re-layering the PNG over the top using AlphaImageLoaded. You can change the name or path of the image in the top of the JavaScript file, where you’ll also find the option to turn off the adding of position: relative to links and fields if you don’t want that.
The script is kicked off with a call to supersleight.init() at the bottom. The scope of the script can be limited to just one part of the page by passing an ID of an element to supersleight.limitTo(). And that’s all there is to it.
Update March 2008: a version of this script as a jQuery plugin is also now available. |
2007 |
Drew McLellan |
drewmclellan |
2007-12-01T00:00:00+00:00 |
https://24ways.org/2007/supersleight-transparent-png-in-ie6/ |
code |
| 181 |
Working With RGBA Colour |
When Tim and I were discussing the redesign of this site last year, one of the clear goals was to have a graphical style without making the pages heavy with a lot of images. When we launched, a lot of people were surprised that the design wasn’t built with PNGs. Instead we’d used RGBA colour values, which is part of the CSS3 specification.
What is RGBA Colour?
We’re all familiar with specifying colours in CSS using by defining the mix of red, green and blue light required to achieve our tone. This is fine and dandy, but whatever values we specify have one thing in common — the colours are all solid, flat, and well, a bit boring.
Flat RGB colours
CSS3 introduces a couple of new ways to specify colours, and one of those is RGBA. The A stands for Alpha, which refers to the level of opacity of the colour, or to put it another way, the amount of transparency. This means that we can set not only the red, green and blue values, but also control how much of what’s behind the colour shows through. Like with layers in Photoshop.
Don’t We Have Opacity Already?
The ability to set the opacity on a colour differs subtly from setting the opacity on an element using the CSS opacity property. Let’s look at an example.
Here we have an H1 with foreground and background colours set against a page with a patterned background.
Heading with no transparency applied
h1 {
color: rgb(0, 0, 0);
background-color: rgb(255, 255, 255);
}
By setting the CSS opacity property, we can adjust the transparency of the entire element and its contents:
Heading with 50% opacity on the element
h1 {
color: rgb(0, 0, 0);
background-color: rgb(255, 255, 255);
opacity: 0.5;
}
RGBA colour gives us something different – the ability to control the opacity of the individual colours rather than the entire element. So we can set the opacity on just the background:
50% opacity on just the background colour
h1 {
color: rgb(0, 0, 0);
background-color: rgba(255, 255, 255, 0.5);
}
Or leave the background solid and change the opacity on just the text:
50% opacity on just the foreground colour
h1 {
color: rgba(0, 0, 0, 0.5);
background-color: rgb(255, 255, 255);
}
The How-To
You’ll notice that above I’ve been using the rgb() syntax for specifying colours. This is a bit less common than the usual hex codes (like #FFF) but it makes sense when starting to use RGBA. As there’s no way to specify opacity with hex codes, we use rgba() like so:
color: rgba(255, 255, 255, 0.5);
Just like rgb() the first three values are red, green and blue. You can specify these 0-255 or 0%-100%. The fourth value is the opacity level from 0 (completely transparent) to 1 (completely opaque).
You can use this anywhere you’d normally set a colour in CSS — so it’s good for foregrounds and background, borders, outlines and so on. All the transparency effects on this site’s current design are achieved this way.
Supporting All Browsers
Like a lot of the features we’ll be looking at in this year’s 24 ways, RGBA colour is supported by a lot of the newest browsers, but not the rest. Firefox, Safari, Chrome and Opera browsers all support RGBA, but Internet Explorer does not.
Fortunately, due to the robust design of CSS as a language, we can specify RGBA colours for browsers that support it and an alternative for browsers that do not.
Falling back to solid colour
The simplest technique is to allow the browser to fall back to using a solid colour when opacity isn’t available. The CSS parsing rules specify that any unrecognised value should be ignored. We can make use of this because a browser without RGBA support will treat a colour value specified with rgba() as unrecognised and discard it.
So if we specify the colour first using rgb() for all browsers, we can then overwrite it with an rgba() colour for browsers that understand RGBA.
h1 {
color: rgb(127, 127, 127);
color: rgba(0, 0, 0, 0.5);
}
Falling back to a PNG
In cases where you’re using transparency on a background-color (although not on borders or text) it’s possible to fall back to using a PNG with alpha channel to get the same effect. This is less flexible than using CSS as you’ll need to create a new PNG for each level of transparency required, but it can be a useful solution.
Using the same principal as before, we can specify the background in a style that all browsers will understand, and then overwrite it in a way that browsers without RGBA support will ignore.
h1 {
background: transparent url(black50.png);
background: rgba(0, 0, 0, 0.5) none;
}
It’s important to note that this works because we’re using the background shorthand property, enabling us to set both the background colour and background image in a single declaration. It’s this that enables us to rely on the browser ignoring the second declaration when it encounters the unknown rgba() value.
Next Steps
The really great thing about RGBA colour is that it gives us the ability to create far more graphically rich designs without the need to use images. Not only does that make for faster and lighter pages, but sites which are easier and quicker to build and maintain. CSS values can also be changed in response to user interaction or even manipulated with JavaScript in a way that’s just not so easy using images.
Opacity can be changed on :hover or manipulated with JavaScript
div {
color: rgba(255, 255, 255, 0.8);
background-color: rgba(142, 213, 87, 0.3);
}
div:hover {
color: rgba(255, 255, 255, 1);
background-color: rgba(142, 213, 87, 0.6);
}
Clever use of transparency in border colours can help ease the transition between overlay items and the page behind.
Borders can receive the RGBA treatment, too
div {
color: rgb(0, 0, 0);
background-color: rgb(255, 255, 255);
border: 10px solid rgba(255, 255, 255, 0.3);
}
In Conclusion
That’s a brief insight into RGBA colour, what it’s good for and how it can be used whilst providing support for older browsers. With the current lack of support in Internet Explorer, it’s probably not a technique that commercial designs will want to heavily rely on right away – simply because of the overhead of needing to think about fallback all the time.
It is, however, a useful tool to have for those smaller, less critical touches that can really help to finesse a design. As browser support becomes more mainstream, you’ll already be familiar and practised with RGBA and ready to go. |
2009 |
Drew McLellan |
drewmclellan |
2009-12-01T00:00:00+00:00 |
https://24ways.org/2009/working-with-rgba-colour/ |
code |
| 220 |
Finding Your Way with Static Maps |
Since the introduction of the Google Maps service in 2005, online maps have taken off in a way not really possible before the invention of slippy map interaction. Although quickly followed by a plethora of similar services from both commercial and non-commercial parties, Google’s first-mover advantage, and easy-to-use developer API saw Google Maps become pretty much the de facto mapping service.
It’s now so easy to add a map to a web page, there’s no reason not to. Dropping an iframe map into your page is as simple as embedding a YouTube video.
But there’s one crucial drawback to both the solution Google provides for you to drop into your page and the code developers typically implement themselves – they don’t work without JavaScript.
A bit about JavaScript
Back in October of this year, The Yahoo! Developer Network blog ran some tests to measure how many visitors to the Yahoo! home page didn’t have JavaScript available or enabled in their browser. It’s an interesting test when you consider that the audience for the Yahoo! home page (one of the most visited pages on the web) represents about as mainstream a sample as you’ll find. If there’s any such thing as an ‘average Web user’ then this is them.
The results surprised me. It varied from region to region, but at most just two per cent of visitors didn’t have JavaScript running. To be honest, I was expecting it to be higher, but this quote from the article caught my attention:
While the percentage of visitors with JavaScript disabled seems like a low number, keep in mind that small percentages of big numbers are also big numbers.
That’s right, of course, and it got me thinking about what that two per cent means. For many sites, two per cent is the number of visitors using the Opera web browser, using IE6, or using Mobile Safari.
So, although a small percentage of the total, users without JavaScript can’t just be forgotten about, and catering for them is at the very heart of how the web is supposed to work.
Starting with content in HTML, we layer on presentation with CSS and then enhance interactivity with JavaScript. If anything fails along the way or the network craps out, or a browser just doesn’t support one of the technologies, the user still gets something they can work with.
It’s progressive enhancement – also known as doing our jobs properly.
Sorry, wasn’t this about maps?
As I was saying, the default code Google provides, and the example code it gives to developers (which typically just gets followed ‘as is’) doesn’t account for users without JavaScript. No JavaScript, no content.
When adding the ability to publish maps to our small content management system Perch, I didn’t want to provide a solution that only worked with JavaScript. I had to go looking for a way to provide maps without JavaScript, too.
There’s a simple solution, fortunately, in the form of static map tiles. All the various slippy map services use a JavaScript interface on top of what are basically rendered map image tiles. Dragging the map loads in more image tiles in the direction you want to view. If you’ve used a slippy map on a slow connection, you’ll be familiar with seeing these tiles load in one by one.
The Static Map API
The good news is that these tiles (or tiles just like them) can be used as regular images on your site. Google has a Static Map API which not only gives you a handy interface to retrieve a tile for the exact area you need, but also allows you to place pins, and zoom and centre the tile so that the image looks just so.
This means that you can create a static, non-JavaScript version of your slippy map’s initial (or ideal) state to load into your page as a regular image, and then have the JavaScript map hijack the image and make it slippy.
Clearly, that’s not going to be a perfect solution for every map’s requirements. It doesn’t allow for panning, zooming or interrogation without JavaScript. However, for the majority of straightforward map uses online, a static map makes a great alternative for those visitors without JavaScript.
Here’s the how
Retrieving a static map tile is staggeringly easy – it’s just a case of forming a URL with the correct arguments and then using that as the src of an image tag.
<img src="http://maps.google.com/maps/api/staticmap
?center=Bethlehem+Israel
&zoom=5
&size=540x280
&maptype=satellite
&markers=color:red|31.4211,35.1144
&sensor=false"
width="540" height="280" alt="Map of Bethlehem, Israel" />
As you can see, there are a few key options that we pass along to the base URL. All of these should be familiar to anyone who’s worked with the JavaScript API.
center determines the point on which the map is centred. This can be latitude and longitude values, or simply an address which is then geocoded.
zoom sets the zoom level.
size is the pixel dimensions of the image you require.
maptype can be roadmap, satellite, terrain or hybrid.
markers sets one or more pin locations. Markers can be labelled, have different colours, and so on – there’s quite a lot of control available.
sensor states whether you are using a sensor to determine the user’s location. When just embedding a map in a web page, set this to false.
There are many options, including plotting paths and setting the image format, which can all be found in the straightforward documentation.
Adding to your page
If you’ve worked with the JavaScript API, you’ll know that it needs a container element which you inject the map into:
<div id="map"></div>
All you need to do is put your static image inside that container:
<div id="map">
<img src="http://maps.google.com/maps/api/staticmap[...]" />
</div>
And then, in your JavaScript, find the image and remove it. For example, with jQuery you’d simply use:
$('#map img').remove();
Why not use a <noscript> element around the image? You could, and that would certainly work fine for browsers that do not support JavaScript. What that won’t cover, however, is the situation where the browser has JavaScript support but, for whatever reason, the JavaScript doesn’t run. This could be due to network issues, an aggressive corporate firewall, or even just a bug in your code. So for that reason, we put the image in for all browsers that show images, and then remove it when the JavaScript is successfully running.
See an example in action
About rate limits
The Google Static Map API limits the requests per site viewer – currently at one thousand distinct maps per day per viewer. So, for most sites you really don’t need to worry about the rate limit. Requests for the same tile aren’t normally counted, as the tile has already been generated and is cached. You can embed the images direct from Google and let it worry about the distribution and caching.
In conclusion
As you can see, adding a static map alongside your dynamic map for those users without JavaScript is very easy indeed. There may not be a huge percentage of web visitors browsing without JavaScript but, as we’ve seen, a small percentage of a big number is still a big number. When it’s so easy to add a static map, can you really justify not doing it? |
2010 |
Drew McLellan |
drewmclellan |
2010-12-01T00:00:00+00:00 |
https://24ways.org/2010/finding-your-way-with-static-maps/ |
code |
| 264 |
Dynamic Social Sharing Images |
Way back when social media was new, you could be pretty sure that whatever you posted would be read by those who follow you. If you’d written a blog post and you wanted to share it with those who follow you, you could post a link and your followers would see it in their streams. Oh heady days!
With so many social channels and a proliferation of content and promotions flying past in everyone’s streams, it’s no longer enough to share content on social media, you have to actively sell it if you want it to be seen. You really need to make the most of every opportunity to catch a reader’s attention if you’re trying to get as many eyes as possible on that sweet, sweet social content.
One of the best ways to grab attention with your posts or tweets is to include an image. There’s heaps of research that says that having images in your posts helps them stand out to followers. Reports I found showed figures from anything from 35% to 150% improvement from just having image in a post. Unfortunately, the details were surrounded with gross words like engagement and visual marketing assets and so I had to close the page before I started to hate myself too much.
So without hard stats to quote, we’ll call it a rule of thumb. The rule of thumb is that posts with images will grab more attention than those without, so it makes sense that when adding pages to a website, you should make sure that they have social media sharing images associated with them.
Adding sharing images
The process for declaring an image to be used in places like Facebook and Twitter is very simple, and at this point is familiar to many of us. You add a meta tag to the head of the page to point to the location of the image to use. When a link to the page is added to a post, the social network will fetch the page, look for the meta tag and then use the image you specified.
<meta property="og:image" content="https://example.com/my_image.jpg">
There’s a good post on this over at CSS-Tricks if you need to bone up on the details of this and other similar meta tags for social media sharing.
This is all fine and well for content that has a very obvious choice of image to go along with it, but what if you don’t necessarily have an image? One approach is to use stock photography, but that’s not going to be right for every situation.
This was something we faced with 24 ways in 2017. We wanted to add images to the tweets we post each day announcing a new article. Some articles have images, but not all, and there tended not to be any consistency in terms of imagery from one article to the next. We always have an author photograph, but those don’t usually lend themselves directly to being the main ‘hero’ image for an article.
Putting his thinking cap on, Paul came up with a design for an image that used the author photo along with a quote extracted from the article.
One of the hand-made sharing images from 2017
Each day we would pick a quote from the article, and Paul would manually compose an image to be uploaded to the site. The results were great, but the whole process was a bit too labour intensive and relied on an individual (Paul) being available each day to do the work. I thought we could probably improve this.
Hatching a new plan
One initial idea I came up with was to script the image editor to dynamically build a new image by pulling content from our database. Sketch has plugins available to pull JSON content into a design, and our CMS can easily output JSON data, so that was one possibility.
The more I thought about this and how much I wish graphic design tools worked just a little bit more like CSS, the obvious solution hit me. We should just build it with CSS!
In fact, as the author name and image already exist in our CMS, and the visual styling is based on the design of the website, couldn’t this just be another page on the site generated by the CMS?
Breaking it down, I figured the steps needed would be something like:
Create the CSS to lay out a component that could be turned into an image
Add a new field to articles in the CMS to hold a handpicked quote
Build a new article template in the CMS to output the author name and quote dynamically for any article
… um … screenshot?
I thought I’d get cracking and see if I could figure out the final steps later.
Building the page
The first thing to tackle was the basic HTML and CSS to lay out the components for our image. That bit was really easy, as I just asked Paul to do it. Everyone should have a Paul.
Paul’s code uses a fixed dimension container in the HTML, set to 600 × 315px. This is to make it the correct aspect ratio for Facebook’s recommended image size. It’s useful to remember here that it doesn’t need to be responsive or robust, as the page only needs to lay out correctly for a screenshot and a fixed size in a known browser.
With the markup and CSS in place, I turned this into a new template. Our CMS can easily display content through any number of templates, so I created a version of the article template that was totally stripped down. It only included the author details and the quote, along with Paul’s markup.
I also added the quote as a new field on the article in the CMS, so each ‘image’ could be quickly and easily customised in the editing process.
I added a new field to the article template to capture the quote.
With very little effort, we quickly had a page to dynamically generate our ‘image’ right from the CMS. You can see any of them by adding /sharing onto the end of an article URL for any 2018 article.
Our automatically generated layout direct from the CMS
It soon became clear that the elusive Step 4 was going to be the tricky part. I can create a small page on the site that looks like an image, but how should I go about turning it into one? An obvious route is to screenshot the page by hand, but that’s going back to some of the manual steps I was trying to eliminate, and also opens up a possibility for errors to be made. But it did lead me to the thought… how could I automatically take a screenshot?
Enter Puppeteer
Puppeteer is a Node.js library that provides a nice API onto Headless Chrome. What is Headless Chrome, you ask? It’s just a version of the Chrome browser than runs from the command line without ever drawing anything to a user interface window. It loads pages, renders CSS, runs JavaScript, pretty much every normal thing that Chrome on the desktop does, but without a clicky user interface.
Headless Chrome can be used for all sorts of things such as running automated tests on front-end code after making changes, or… get this… rendering pages that can be used for screenshots. The actual process of writing some code to control Chrome and to take the screenshot is where Puppeteer comes in. Puppeteer puts a friendly layer in front of big old scary Chrome to enable us to interact with it using simple JavaScript code running in Node.
Using Puppeteer, I can write a small script that will repeatably turn a URL into an image. So simple is it to do this, that’s it’s actually Puppeteer’s ‘hello world’ example.
First you install Puppeteer. It downloads a compatible headless browser (actually Chromium) as a dependancy, so you don’t need to worry about installing that. At the command line:
npm i puppeteer
Then save a new file as example.js with this code:
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto('https://example.com');
await page.screenshot({path: 'example.png'});
await browser.close();
})();
and then run it using Node:
node example.js
This will output an image file example.png to disk, which contains a screenshot of, in this case https://example.com. The logic of the code is reasonably easy to follow:
Launch a browser
Open up a new page
Goto a URL
Take a screenshot
Close the browser
The async function and await keywords are a way to have the script pause and wait for normally asynchronous code to return before proceeding. That’s useful with actions like loading a web page that might take some time to complete. They’re used with Promises, and the effect is to make asynchronous code behave as if it’s synchronous. You can read more about async and await at MDN if you’re interested.
That’s a good proof-of-concept using the basic Puppeteer example. I can take a screenshot of a URL! But what happens if I put the URL of my new special page in there?
Our content is up in the corner of the image with lots of empty space.
That’s not great. It’s okay, but not great. It looks like that, by default, Puppeteer takes a screenshot with a resolution of 800 × 600, so we need to find out how to adjust that. Fortunately, the docs aren’t the worst and I was able to find the page.setViewport() method pretty easily.
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto('https://24ways.org/2018/clip-paths-know-no-bounds/sharing');
await page.setViewport({
width: 600,
height: 315
});
await page.screenshot({path: 'example.png'});
await browser.close();
})();
This worked! The screenshot is now 600 × 315 as expected. That’s exactly what we asked for. Trouble is, that’s a bit low res and it is nearly 2019 after all. While in those docs, I noticed the deviceScaleFactor option that can be passed to page.setViewport(). Setting that to 2 gives us an image of the same area of the screen, but with twice as many pixels.
await page.setViewport({
width: 600,
height: 315,
deviceScaleFactor: 2
});
Perfect! We now have a programmatic way of turning a URL into an image.
Improving the script
Rather than having a script with a fixed URL in it that outputs an image called example.png, the next step is to make that a bit more dynamic. The aim here is to have a script that we can run with a URL as an argument and have it output an image for that one page. That way we can run it manually, or hook it into part of our site’s build process to automate the generation of the image.
Our goal is to call the script like this:
node shoot-sharing-image.js https://24ways.org/2018/clip-paths-know-no-bounds/
And I want the image to come out with the name clip-paths-know-no-bounds.png. To do that, I need to have my script look for command arguments, and then to split the URL up to grab the slug from it.
// Get the URL and the slug segment from it
const url = process.argv[2];
const segments = url.split('/');
// Get the second-to-last segment (the slug)
const slug = segments[segments.length-2];
We can then use these variables later in the script, remembering to add sharing back onto the end of the URL to get our dedicated page.
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto(url + 'sharing');
await page.setViewport({
width: 600,
height: 315,
deviceScaleFactor: 2
});
await page.screenshot({path: slug + '.png'});
await browser.close();
})();
Once you’re generating the image with Node, there’s all sorts of things you can do with it. An obvious step is to move it to the correct location within your site or project.
You can also run optimisations on the file. I’m using imagemin with pngquant to reduce the file size a little.
const imagemin = require('imagemin');
const imageminPngquant = require('imagemin-pngquant');
await imagemin([slug + '.png'], 'build', {
plugins: [
imageminPngquant({quality: '75-90'})
]
});
You can see the completed example as a gist.
Integrating it with your CMS
So we now have a command we can run to take a URL and generate a custom image for that URL. It’s in a format that can be called by any sort of build script, or triggered from a publishing hook in a CMS. Exactly how you do that is going to depend on the way your site is built and the technology stack you’re using, but it’s likely not too hard as long as you can run a command as part of the process.
For 24 ways this year, I’ve been running the script by hand once each article is ready. My script adds the file to a git repo and pushes to a deployment remote that is configured to automatically deploy static assets to our server. Along with our theme of making incremental improvements, next year I’ll look to automate this one step further.
We may also look at having a few slightly different layouts to choose from, so that each day isn’t exactly the same as the last. Interestingly, we could even try some A/B tests to see if there’s any particular format of image or type of quote that does a better job of grabbing attention. There are lots of possibilities!
By using a bit of ingenuity, some custom CMS templates, and the very useful Puppeteer project, we’ve been able to reliably produce dynamic social media sharing images for all of our articles. In doing so, we reduced the dependancy on any individual for producing those images, and opened up a world of possibilities in how we use those images.
I hope you’ll give it a try! |
2018 |
Drew McLellan |
drewmclellan |
2018-12-24T00:00:00+00:00 |
https://24ways.org/2018/dynamic-social-sharing-images/ |
code |
| 271 |
Creating Custom Font Stacks with Unicode-Range |
Any web designer or front-end developer worth their salt will be familiar with the CSS @font-face rule used for embedding fonts in a web page. We’ve all used it — either directly in our code ourselves, or via one of the web font services like Fontdeck, Typekit or Google Fonts.
If you’re like me, however, you’ll be used to just copying and pasting in a specific incantation of lines designed to get different formats of fonts working in different browsers, and may not have really explored all the capabilities of @font-face properties as defined by the spec.
One such property — the unicode-range descriptor — sounds pretty dull and is easily overlooked. It does, however, have some fairly interesting possibilities when put to use in creative ways.
Unicode-range
The unicode-range descriptor is designed to help when using fonts that don’t have full coverage of the characters used in a page. By adding a unicode-range property to a @font-face rule it is possible to specify the range of characters the font covers.
@font-face {
font-family: BBCBengali;
src: url(fonts/BBCBengali.ttf) format("opentype");
unicode-range: U+00-FF;
}
In this example, the font is to be used for characters in the range of U+00 to U+FF which runs from the unexciting control characters at the start of the Unicode table (symbols like the exclamation mark start at U+21) right through to ÿ at U+FF – the extent of the Basic Latin character range.
By adding multiple @font-face rules for the same family but with different ranges, you can build up complete coverage of the characters your page uses by using different fonts.
When I say that it’s possible to specify the range of characters the font covers, that’s true, but what you’re really doing with the unicode-range property is declaring which characters the font should be used for. This becomes interesting, because instead of merely working with the technical constraints of available characters in a given font, we can start picking and choosing characters to use and selectively mix fonts together.
The best available ampersand
A few years back, Dan Cederholm wrote a post encouraging designers to use the best available ampersand. Dan went on to outline how this can be achieved by wrapping our ampersands in a <span> element with a class applied:
<span class="amp">&</span>
A CSS rule can then be written to select the <span> and apply a different font:
span.amp {
font-family: Baskerville, Palatino, "Book Antiqua", serif;
}
That’s a perfectly serviceable technique, but the drawbacks are clear — you have to add extra markup which is borderline presentational, and you also have to be able to add that markup, which isn’t always possible when working with a CMS.
Perhaps we could do this with unicode-range.
A better best available ampersand
The Unicode code point for an ampersand is U+26, so the ampersand font stack above can be created like so:
@font-face {
font-family: 'Ampersand';
src: local('Baskerville'), local('Palatino'), local('Book Antiqua');
unicode-range: U+26;
}
What we’ve done here is specify a new family called Ampersand and created a font stack for it with the user’s locally installed copies of Baskerville, Palatino or Book Antiqua. We’ve then limited it to a single character range — the ampersand. Of course, those don’t need to be local fonts — they could be web font files, too. If you have a font with a really snazzy ampersand, go for your life.
We can then use that new family in a regular font stack.
h1 {
font-family: Ampersand, Arial, sans-serif;
}
With this in place, any <h1> elements in our page will use the Ampersand family (Baskerville, Palatino or Book Antiqua) for ampersands, and Arial for all other characters. If the user doesn’t have any of the Ampersand family fonts available, the ampersand will fall back to the next item in the font stack, Arial.
You didn’t think it was that easy, did you?
Oh, if only it were so. The problem comes, as ever, with the issue of browser support. The unicode-range property has good support in WebKit browsers (like Safari and Chrome, and the browsers on most popular smartphone platforms) and in recent versions of Internet Explorer. The big stumbling block comes in the form of Firefox, which has no support at all.
If you’re familiar with how CSS works when it comes to unsupported properties, you’ll know that if a browser encounters a property it doesn’t implement, it just skips that declaration and moves on to the next. That works perfectly for things like border-radius — if the browser can’t round off the corners, the declaration is skipped and the user sees square corners instead. Perfect.
Less perfect when it comes to unicode-range, because if no range is specified then the default is that the font is applied for all characters — the whole range. If you’re using a fancy font for flamboyant ampersands, you probably don’t want that applied to all your text if unicode-range isn’t supported. That would be bad. Really bad.
Ensuring good fallbacks
As ever, the trick is to make sure that there’s a sensible fallback in place if a browser doesn’t have support for whatever technology you’re trying to use. This is where being a super nerd about understanding the spec you’re working with really pays off.
We can make use of the rules of the CSS cascade to make sure that if unicode-range isn’t supported we get a sensible fallback font. What would be ideal is if we were able to follow up the @font-face rule with a second rule to override it if Unicode ranges aren’t implemented.
@font-face {
font-family: 'Ampersand';
src: local('Baskerville'), local('Palatino'), local('Book Antiqua');
unicode-range: U+26;
}
@font-face {
font-family: 'Ampersand';
src: local('Arial');
}
In theory, this code should make sense for all browsers. For those that support unicode-range the two rules become cumulative. They specify different ranges for the same family, and in WebKit browsers this has the expected result of using Arial for most characters, but Baskerville and friends for the ampersand. For browsers that don’t have support, the second rule should just supersede the first, setting the font to Arial.
Unfortunately, this code causes current versions of Firefox to freak out and use the first rule, applying Baskerville to the entire range. That’s both unexpected and unfortunate. Bad Firefox. On your rug.
If that doesn’t work, what can we do? Well, we know that if given a unicode-range Firefox will ignore the range and apply the font to all characters. That’s really what we’re trying to achieve. So what if we specified a range for the fallback font, but made sure it only covers some obscure high-value Unicode character we’re never going to use in our page? Then it wouldn’t affect the outcome for browsers that do support ranges.
@font-face {
font-family: 'Ampersand';
src: local('Baskerville'), local('Palatino'), local('Book Antiqua');
unicode-range: U+26;
}
@font-face {
/* Ampersand fallback font */
font-family: 'Ampersand';
src: local('Arial');
unicode-range: U+270C;
}
By specifying a range on the fallback font, Firefox appears to correctly override the first based on the cascade sort order. Browsers that do support ranges take the second rule in addition, and apply Arial for that obscure character we’re not using in any of our pages — U+270C.
So we get our nice ampersands in browsers that support unicode-range and, thanks to our styling of an obscure Unicode character, the font falls back to a perfectly acceptable Arial in browsers that do not offer support. Perfect!
That obscure character, my friends, is what Unicode defines as the VICTORY HAND.
✌
So, how can we use this?
Ampersands are a neat trick, and it works well in browsers that support ranges, but that’s not really the point of all this. Styling ampersands is fun, but they’re only really scratching the surface. Consider more involved examples, such as substituting a different font for numerals, or symbols, or even caps. Things certainly begin to get a bit more interesting.
How do you know what the codes are for different characters? Richard Ishida has a handy online conversion tool available where you can type in the characters and get the Unicode code points out the other end.
Of course, the fact remains that browser support for unicode-range is currently limited, so any application needs to have fallbacks that you’re still happy for a significant proportion of your visitors to see. In some cases, such as dedicated pages for mobile devices in an HTML-based phone app, this is immediately useful as support in WebKit browsers is already very good. In other cases, you’ll have to use your own best judgement based on your needs and audience.
One thing to keep in mind is that if you’re using web fonts, the entire font will be downloaded even if only one character is used. That said, the font shouldn’t be downloaded if none of the characters within the Unicode range are present in a given page.
As ever, there are pros and cons to using unicode-range as well as varied but increasing support in browsers. It remains a useful tool to understand and have in your toolkit for when the right moment comes along. |
2011 |
Drew McLellan |
drewmclellan |
2011-12-01T00:00:00+00:00 |
https://24ways.org/2011/creating-custom-font-stacks-with-unicode-range/ |
code |
| 300 |
Taking Device Orientation for a Spin |
When The Police sang “Don’t Stand So Close To Me” they weren’t talking about using a smartphone to view a panoramic image on Facebook, but they could have been. For years, technology has driven relentlessly towards devices we can carry around in our pockets, and now that we’re there, we’re expected to take the thing out of our pocket and wave it around in front of our faces like a psychotic donkey in search of its own dangly carrot.
But if you can’t beat them, join them.
A brave new world
A couple of years back all sorts of specs for new HTML5 APIs sprang up much to our collective glee. Emboldened, we ran a few tests and found they basically didn’t work in anything and went off disheartened into the corner for a bit of a sob.
Turns out, while we were all busy boohooing, those browser boffins have actually being doing some work, and lo and behold, some of these APIs are even half usable. Mostly literally half usable—we’re still talking about browsers, after all.
Now, of course they’re all a bit JavaScripty and are going to involve complex methods and maths and science and probably about a thousand dependancies from Github that will fall out of fashion while we’re still trying to locate the documentation, right? Well, no!
So what if we actually wanted to use one of these APIs, say to impress our friends with our ability to make them wave their phones in front of their faces (because no one enjoys looking hapless more than the easily-technologically-impressed), how could we do something like that? Let’s find out.
The Device Orientation API
The phone-wavy API is more formally known as the DeviceOrientation Event Specification. It does a bunch of stuff that basically doesn’t work, but also gives us three values that represent orientation of a device (a phone, a tablet, probably not a desktop computer) around its x, y and z axes. You might think of it as pitch, roll and yaw if you like to spend your weekends wearing goggles and a leather hat.
The main way we access these values is through an event listener, which can inform our code every time the value changes. Which is constantly, because you try and hold a phone still and then try and hold the Earth still too.
The API calls those pitch, roll and yaw values alpha, beta and gamma. Chocks away:
window.addEventListener('deviceorientation', function(e) {
console.log(e.alpha);
console.log(e.beta);
console.log(e.gamma);
});
If you look at this test page on your phone, you should be able to see the numbers change as you twirl the thing around your body like the dance partner you never had. Wrist strap recommended.
One important note
Like may of these newfangled APIs, Device Orientation is only available over HTTPS. We’re not allowed to have too much fun without protection, so make sure that you’re working on a secure line. I’ve found a quick and easy way to share my local dev environment over TLS with my devices is to use an ngrok tunnel.
ngrok http -host-header=rewrite mylocaldevsite.dev:80
ngrok will then set up a tunnel to your dev site with both HTTP and HTTPS URL options. You, of course, want the HTTPS option.
Right, where were we?
Make something to look at
It’s all well and good having a bunch of numbers, but they’re no use unless we do something with them. Something creative. Something to inspire the generations. Or we could just build that Facebook panoramic image viewer thing (because most of us are familiar with it and we’re not trying to be too clever here). Yeah, let’s just build one of those.
Our basic framework is going to be similar to that used for an image carousel. We have a container, constrained in size, and CSS overflow property set to hidden. Into this we place our wide content and use positioning to move the content back and forth behind the ‘window’ so that the part we want to show is visible.
Here it is mocked up with a slider to set the position. When you release the slider, the position updates. (This actually tests best on desktop with your window slightly narrowed.)
The details of the slider aren’t important (we’re about to replace it with phone-wavy goodness) but the crucial part is that moving the slider results in a function call to position the image. This takes a percentage value (0-100) with 0 being far left and 100 being far right (or ‘alt-nazi’ or whatever).
var position_image = function(percent) {
var pos = (img_W / 100)*percent;
img.style.transform = 'translate(-'+pos+'px)';
};
All this does is figure out what that percentage means in terms of the image width, and set the transform: translate(…); CSS property to move the image. (We use translate because it might be a bit faster to animate than left/right positioning.)
Ok. We can now read the orientation values from our device, and we can programatically position the image. What we need to do is figure out how to convert those raw orientation values into a nice tidy percentage to pass to our function and we’re done. (We’re so not done.)
The maths bit
If we go back to our raw values test page and make-believe that we have a fascinating panoramic image of some far-off beach or historic monument to look at, you’ll note that the main value that is changing as we swing back and forth is the ‘alpha’ value. That’s the one we want to track.
As our goal here is hey, these APIs are interesting and fun and not let’s build the world’s best panoramic image viewer, we’ll start by making a few assumptions and simplifications:
When the image loads, we’ll centre the image and take the current nose-forward orientation reading as the middle.
Moving left, we’ll track to the left of the image (lower percentage).
Moving right, we’ll track to the right (higher percentage).
If the user spins round, does cartwheels or loads the page then hops on a plane and switches earthly hemispheres, they’re on their own.
Nose-forward
When the page loads, the initial value of alpha gives us our nose-forward position. In Safari on iOS, this is normalised to always be 0, whereas most everywhere else it tends to be bound to pointy-uppy north. That doesn’t really matter to us, as we don’t know which direction the user might be facing in anyway — we just need to record that initial state and then use it to compare any new readings.
var initial_position = null;
window.addEventListener('deviceorientation', function(e) {
if (initial_position === null) {
initial_position = Math.floor(e.alpha);
};
var current_position = initial_position - Math.floor(e.alpha);
});
(I’m rounding down the values with Math.floor() to make debugging easier - we’ll take out the rounding later.)
We get our initial position if it’s not yet been set, and then calculate the current position as a difference between the new value and the stored one.
These values are weird
One thing you need to know about these values, is that they range from 0 to 360 but then you also get weird left-of-zero values like -2 and whatever. And they wrap past 360 back to zero as you’d expect if you do a forward roll.
What I’m interested in is working out my rotation. If 0 is my nose-forward position, I want a positive value as I turn right, and a negative value as I turn left. That puts the awkward 360-tipping point right behind the user where they can’t see it.
var rotation = current_position;
if (current_position > 180) rotation = current_position-360;
Which way up?
Since we’re talking about orientation, we need to remember that the values are going to be different if the device is held in portrait on landscape mode. See for yourself - wiggle it like a steering wheel and you get different values. That’s easy to account for when you know which way up the device is, but in true browser style, the API for that bit isn’t well supported. The best I can come up with is:
var screen_portrait = false;
if (window.innerWidth < window.innerHeight) {
screen_portrait = true;
}
It works. Then we can use screen_portrait to branch our code:
if (screen_portrait) {
if (current_position > 180) rotation = current_position-360;
} else {
if (current_position < -180) rotation = 360+current_position;
}
Here’s the code in action so you can see the values for yourself. If you change screen orientation you’ll need to refresh the page (it’s a demo!).
Limiting rotation
Now, while the youth of today are rarely seen without a phone in their hands, it would still be unreasonable to ask them to spin through 360° to view a photo. Instead, we need to limit the range of movement to something like 60°-from-nose in either direction and normalise our values to pan the entire image across that 120° range. -60 would be full-left (0%) and 60 would be full-right (100%).
If we set max_rotation = 60, that code ends up looking like this:
if (rotation > max_rotation) rotation = max_rotation;
if (rotation < (0-max_rotation)) rotation = 0-max_rotation;
var percent = Math.floor(((rotation + max_rotation)/(max_rotation*2))*100);
We should now be able to get a rotation from -60° to +60° expressed as a percentage. Try it for yourself.
The big reveal
All that’s left to do is pass that percentage to our image positioning function and would you believe it, it might actually work.
position_image(percent);
You can see the final result and take it for a spin. Literally.
So what have we made here? Have we built some highly technical panoramic image viewer to aid surgeons during life-saving operations using only JavaScript and some slightly questionable mathematics? No, my friends, we have not. Far from it.
What we have made is progress. We’ve taken a relatively newly available hardware API and a bit of simple JavaScript and paired it with existing CSS knowledge and made something that we didn’t have this morning. Something we probably didn’t even want this morning. Something that if you take a couple of steps back and squint a bit might be a prototype for something vaguely interesting. But more importantly, we’ve learned that our browsers are just a little bit more capable than we thought.
The web platform is maturing rapidly. There are new, relatively unexplored APIs for doing all sorts of crazy thing that are often dismissed as the preserve of native apps. Like some sort of app marmalade. Poppycock.
The web is an amazing, exciting place to create things. All it takes is some base knowledge of the fundamentals, a creative mind and a willingness to learn. We have those! So let’s create things. |
2016 |
Drew McLellan |
drewmclellan |
2016-12-24T00:00:00+00:00 |
https://24ways.org/2016/taking-device-orientation-for-a-spin/ |
code |
| 314 |
Easy Ajax with Prototype |
There’s little more impressive on the web today than a appropriate touch of Ajax. Used well, Ajax brings a web interface much closer to the experience of a desktop app, and can turn a bear of an task into a pleasurable activity.
But it’s really hard, right? It involves all the nasty JavaScript that no one ever does often enough to get really good at, and the browser support is patchy, and urgh it’s just so much damn effort. Well, the good news is that – ta-da – it doesn’t have to be a headache. But man does it still look impressive. Here’s how to amaze your friends.
Introducing prototype.js
Prototype is a JavaScript framework by Sam Stephenson designed to help make developing dynamic web apps a whole lot easier. In basic terms, it’s a JavaScript file which you link into your page that then enables you to do cool stuff.
There’s loads of capability built in, a portion of which covers our beloved Ajax. The whole thing is freely distributable under an MIT-style license, so it’s good to go. What a nice man that Mr Stephenson is – friends, let us raise a hearty cup of mulled wine to his good name. Cheers! sluurrrrp.
First step is to download the latest Prototype and put it somewhere safe. I suggest underneath the Christmas tree.
Cutting to the chase
Before I go on and set up an example of how to use this, let’s just get to the crux. Here’s how Prototype enables you to make a simple Ajax call and dump the results back to the page:
var url = 'myscript.php';
var pars = 'foo=bar';
var target = 'output-div';
var myAjax = new Ajax.Updater(target, url, {method: 'get', parameters: pars});
This snippet of JavaScript does a GET to myscript.php, with the parameter foo=bar, and when a result is returned, it places it inside the element with the ID output-div on your page.
Knocking up a basic example
So to get this show on the road, there are three files we need to set up in our site alongside prototype.js. Obviously we need a basic HTML page with prototype.js linked in. This is the page the user interacts with. Secondly, we need our own JavaScript file for the glue between the interface and the stuff Prototype is doing. Lastly, we need the page (a PHP script in my case) that the Ajax is going to make its call too.
So, to that basic HTML page for the user to interact with. Here’s one I found whilst out carol singing:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Easy Ajax</title>
<script type="text/javascript" src="prototype.js"></script>
<script type="text/javascript" src="ajax.js"></script>
</head>
<body>
<form method="get" action="greeting.php" id="greeting-form">
<div>
<label for="greeting-name">Enter your name:</label>
<input id="greeting-name" type="text" />
<input id="greeting-submit" type="submit" value="Greet me!" />
</div>
<div id="greeting"></div>
</form>
</body>
</html>
As you can see, I’ve linked in prototype.js, and also a file called ajax.js, which is where we’ll be putting our glue. (Careful where you leave your glue, kids.)
Our basic example is just going to take a name and then echo it back in the form of a seasonal greeting. There’s a form with an input field for a name, and crucially a DIV (greeting) for the result of our call. You’ll also notice that the form has a submit button – this is so that it can function as a regular form when no JavaScript is available. It’s important not to get carried away and forget the basics of accessibility.
Meanwhile, back at the server
So we need a script at the server which is going to take input from the Ajax call and return some output. This is normally where you’d hook into a database and do whatever transaction you need to before returning a result. To keep this as simple as possible, all this example here will do is take the name the user has given and add it to a greeting message. Not exactly Web 2-point-HoHoHo, but there you have it.
Here’s a quick PHP script – greeting.php – that Santa brought me early.
<?php
$the_name = htmlspecialchars($_GET['greeting-name']);
echo "<p>Season's Greetings, $the_name!</p>";
?>
You’ll perhaps want to do something a little more complex within your own projects. Just sayin’.
Gluing it all together
Inside our ajax.js file, we need to hook this all together. We’re going to take advantage of some of the handy listener routines and such that Prototype also makes available. The first task is to attach a listener to set the scene once the window has loaded. He’s how we attach an onload event to the window object and get it to call a function named init():
Event.observe(window, 'load', init, false);
Now we create our init() function to do our evil bidding. Its first job of the day is to hide the submit button for those with JavaScript enabled. After that, it attaches a listener to watch for the user typing in the name field.
function init(){
$('greeting-submit').style.display = 'none';
Event.observe('greeting-name', 'keyup', greet, false);
}
As you can see, this is going to make a call to a function called greet() onkeyup in the greeting-name field. That function looks like this:
function greet(){
var url = 'greeting.php';
var pars = 'greeting-name='+escape($F('greeting-name'));
var target = 'greeting';
var myAjax = new Ajax.Updater(target, url, {method: 'get', parameters: pars});
}
The key points to note here are that any user input needs to be escaped before putting into the parameters so that it’s URL-ready. The target is the ID of the element on the page (a DIV in our case) which will be the recipient of the output from the Ajax call.
That’s it
No, seriously. That’s everything. Try the example. Amaze your friends with your 1337 Ajax sk1llz. |
2005 |
Drew McLellan |
drewmclellan |
2005-12-01T00:00:00+00:00 |
https://24ways.org/2005/easy-ajax-with-prototype/ |
code |
| 315 |
Edit-in-Place with Ajax |
Back on day one we looked at using the Prototype library to take all the hard work out of making a simple Ajax call. While that was fun and all, it didn’t go that far towards implementing something really practical. We dipped our toes in, but haven’t learned to swim yet.
So here is swimming lesson number one. Anyone who’s used Flickr to publish their photos will be familiar with the edit-in-place system used for quickly amending titles and descriptions on photographs. Hovering over an item turns its background yellow to indicate it is editable. A simple click loads the text into an edit box, right there on the page.
Prototype includes all sorts of useful methods to help reproduce something like this for our own projects. As well as the simple Ajax GETs we learned how to do last time, we can also do POSTs (which we’ll need here) and a whole bunch of manipulations to the user interface – all through simple library calls. Here’s what we’re building, so let’s do it.
Getting Started
There are two major components to this process; the user interface manipulation and the Ajax call itself. Our set-up is much the same as last time (you may wish to read the first article if you’ve not already done so). We have a basic HTML page which links in the prototype.js file and our own editinplace.js. Here’s what Santa dropped down my chimney:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Edit-in-Place with Ajax</title>
<link href="editinplace.css" rel="Stylesheet" type="text/css" />
<script src="prototype.js" type="text/javascript"></script>
<script src="editinplace.js" type="text/javascript"></script>
</head>
<body>
<h1>Edit-in-place</h1>
<p id="desc">Dashing through the snow on a one horse open sleigh.</p>
</body>
</html>
So that’s our page. The editable item is going to be the <p> called desc. The process goes something like this:
Highlight the area onMouseOver
Clear the highlight onMouseOut
If the user clicks, hide the area and replace with a <textarea> and buttons
Remove all of the above if the user cancels the operation
When the Save button is clicked, make an Ajax POST and show that something’s happening
When the Ajax call comes back, update the page with the new content
Events and Highlighting
The first step is to offer feedback to the user that the item is editable. This is done by shading the background colour when the user mouses over. Of course, the CSS :hover pseudo class is a straightforward way to do this, but for three reasons, I’m using JavaScript to switch class names.
:hover isn’t supported on many elements in Internet Explorer for Windows
I want to keep control over when the highlight switches off after an update, regardless of mouse position
If JavaScript isn’t available we don’t want to end up with the CSS suggesting it might be
With this in mind, here’s how editinplace.js starts:
Event.observe(window, 'load', init, false);
function init(){
makeEditable('desc');
}
function makeEditable(id){
Event.observe(id, 'click', function(){edit($(id))}, false);
Event.observe(id, 'mouseover', function(){showAsEditable($(id))}, false);
Event.observe(id, 'mouseout', function(){showAsEditable($(id), true)}, false);
}
function showAsEditable(obj, clear){
if (!clear){
Element.addClassName(obj, 'editable');
}else{
Element.removeClassName(obj, 'editable');
}
}
The first line attaches an onLoad event to the window, so that the function init() gets called once the page has loaded. In turn, init() sets up all the items on the page that we want to make editable. In this example I’ve just got one, but you can add as many as you like.
The function madeEditable() attaches the mouseover, mouseout and click events to the item we’re making editable. All showAsEditable does is add and remove the class name editable from the object. This uses the particularly cunning methods Element.addClassName() and Element.removeClassName() which enable you to cleanly add and remove effects without affecting any styling the object may otherwise have.
Oh, remember to add a rule for .editable to your style sheet:
.editable{
color: #000;
background-color: #ffffd3;
}
The Switch
As you can see above, when the user clicks on an editable item, a call is made to the function edit(). This is where we switch out the static item for a nice editable textarea. Here’s how that function looks.
function edit(obj){
Element.hide(obj);
var textarea ='<div id="' + obj.id + '_editor">
<textarea id="' + obj.id + '_edit" name="' + obj.id + '" rows="4" cols="60">'
+ obj.innerHTML + '</textarea>';
var button = '<input id="' + obj.id + '_save" type="button" value="SAVE" /> OR
<input id="' + obj.id + '_cancel" type="button" value="CANCEL" /></div>';
new Insertion.After(obj, textarea+button);
Event.observe(obj.id+'_save', 'click', function(){saveChanges(obj)}, false);
Event.observe(obj.id+'_cancel', 'click', function(){cleanUp(obj)}, false);
}
The first thing to do is to hide the object. Prototype comes to the rescue with Element.hide() (and of course, Element.show() too). Following that, we build up the textarea and buttons as a string, and then use Insertion.After() to place our new editor underneath the (now hidden) editable object.
The last thing to do before we leave the user to edit is it attach listeners to the Save and Cancel buttons to call either the saveChanges() function, or to cleanUp() after a cancel.
In the event of a cancel, we can clean up behind ourselves like so:
function cleanUp(obj, keepEditable){
Element.remove(obj.id+'_editor');
Element.show(obj);
if (!keepEditable) showAsEditable(obj, true);
}
Saving the Changes
This is where all the Ajax fun occurs. Whilst the previous article introduced Ajax.Updater() for simple Ajax calls, in this case we need a little bit more control over what happens once the response is received. For this purpose, Ajax.Request() is perfect. We can use the onSuccess and onFailure parameters to register functions to handle the response.
function saveChanges(obj){
var new_content = escape($F(obj.id+'_edit'));
obj.innerHTML = "Saving...";
cleanUp(obj, true);
var success = function(t){editComplete(t, obj);}
var failure = function(t){editFailed(t, obj);}
var url = 'edit.php';
var pars = 'id=' + obj.id + '&content=' + new_content;
var myAjax = new Ajax.Request(url, {method:'post',
postBody:pars, onSuccess:success, onFailure:failure});
}
function editComplete(t, obj){
obj.innerHTML = t.responseText;
showAsEditable(obj, true);
}
function editFailed(t, obj){
obj.innerHTML = 'Sorry, the update failed.';
cleanUp(obj);
}
As you can see, we first grab in the contents of the textarea into the variable new_content. We then remove the editor, set the content of the original object to “Saving…” to show that an update is occurring, and make the Ajax POST.
If the Ajax fails, editFailed() sets the contents of the object to “Sorry, the update failed.” Admittedly, that’s not a very helpful way to handle the error but I have to limit the scope of this article somewhere. It might be a good idea to stow away the original contents of the object (obj.preUpdate = obj.innerHTML) for later retrieval before setting the content to “Saving…”. No one likes a failure – especially a messy one.
If the Ajax call is successful, the server-side script returns the edited content, which we then place back inside the object from editComplete, and tidy up.
Meanwhile, back at the server
The missing piece of the puzzle is the server-side script for committing the changes to your database. Obviously, any solution I provide here is not going to fit your particular application. For the purposes of getting a functional demo going, here’s what I have in PHP.
<?php
$id = $_POST['id'];
$content = $_POST['content'];
echo htmlspecialchars($content);
?>
Not exactly rocket science is it? I’m just catching the content item from the POST and echoing it back. For your application to be useful, however, you’ll need to know exactly which record you should be updating. I’m passing in the ID of my <div>, which is not a fat lot of use. You can modify saveChanges() to post back whatever information your app needs to know in order to process the update.
You should also check the user’s credentials to make sure they have permission to edit whatever it is they’re editing. Basically the same rules apply as with any script in your application.
Limitations
There are a few bits and bobs that in an ideal world I would tidy up. The first is the error handling, as I’ve already mentioned. The second is that from an idealistic standpoint, I’d rather not be using innerHTML. However, the reality is that it’s presently the most efficient way of making large changes to the document. If you’re serving as XML, remember that you’ll need to replace these with proper DOM nodes.
It’s also important to note that it’s quite difficult to make something like this universally accessible. Whenever you start updating large chunks of a document based on user interaction, a lot of non-traditional devices don’t cope well. The benefit of this technique, though, is that if JavaScript is unavailable none of the functionality gets implemented at all – it fails silently. It is for this reason that this shouldn’t be used as a complete replacement for a traditional, universally accessible edit form. It’s a great time-saver for those with the ability to use it, but it’s no replacement.
See it in action
I’ve put together an example page using the inert PHP script above. That is to say, your edits aren’t committed to a database, so the example is reset when the page is reloaded. |
2005 |
Drew McLellan |
drewmclellan |
2005-12-23T00:00:00+00:00 |
https://24ways.org/2005/edit-in-place-with-ajax/ |
code |
| 318 |
Auto-Selecting Navigation |
In the article Centered Tabs with CSS Ethan laid out a tabbed navigation system which can be centred on the page. A frequent requirement for any tab-based navigation is to be able to visually represent the currently selected tab in some way.
If you’re using a server-side language such as PHP, it’s quite easy to write something like class="selected" into your markup, but it can be even simpler than that.
Let’s take the navigation div from Ethan’s article as an example.
<div id="navigation">
<ul>
<li><a href="#"><span>Home</span></a></li>
<li><a href="#"><span>About</span></a></li>
<li><a href="#"><span>Our Work</span></a></li>
<li><a href="#"><span>Products</span></a></li>
<li class="last"><a href="#"><span>Contact Us</span></a></li>
</ul>
</div>
As you can see we have a standard unordered list which is then styled with CSS to look like tabs. By giving each tab a class which describes it’s logical section of the site, if we were to then apply a class to the body tag of each page showing the same, we could write a clever CSS selector to highlight the correct tab on any given page.
Sound complicated? Well, it’s not a trivial concept, but actually applying it is dead simple.
Modifying the markup
First thing is to place a class name on each li in the list:
<div id="navigation">
<ul>
<li class="home"><a href="#"><span>Home</span></a></li>
<li class="about"><a href="#"><span>About</span></a></li>
<li class="work"><a href="#"><span>Our Work</span></a></li>
<li class="products"><a href="#"><span>Products</span></a></li>
<li class="last contact"><a href="#"><span>Contact Us</span></a></li>
</ul>
</div>
Then, on each page of your site, apply the a matching class to the body tag to indicate which section of the site that page is in. For example, on your About page:
<body class="about">...</body>
Writing the CSS selector
You can now write a single CSS rule to match the selected tab on any given page. The logic is that you want to match the ‘about’ tab on the ‘about’ page and the ‘products’ tab on the ‘products’ page, so the selector looks like this:
body.home #navigation li.home,
body.about #navigation li.about,
body.work #navigation li.work,
body.products #navigation li.products,
body.contact #navigation li.contact{
... whatever styles you need to show the tab selected ...
}
So all you need to do when you create a new page in your site is to apply a class to the body tag to say which section it’s in. The CSS will do the rest for you – without any server-side help. |
2005 |
Drew McLellan |
drewmclellan |
2005-12-10T00:00:00+00:00 |
https://24ways.org/2005/auto-selecting-navigation/ |
code |
| 336 |
Practical Microformats with hCard |
You’ve probably heard about microformats over the last few months. You may have even read the easily digestible introduction at Digital Web Magazine, but perhaps you’ve not found time to actually implement much yet. That’s understandable, as it can sometimes be difficult to see exactly what you’re adding by applying a microformat to a page. Sure, you’re semantically enhancing the information you’re marking up, and the Semantic Web is a great idea and all, but what benefit is it right now, today?
Well, the answer to that question is simple: you’re adding lots of information that can be and is being used on the web here and now. The big ongoing battle amongst the big web companies if one of territory over information. Everyone’s grasping for as much data as possible. Some of that information many of us are cautious to give away, but a lot of is happy to be freely available. Of the data you’re giving away, it makes sense to give it as much meaning as possible, thus enabling anyone from your friends and family to the giant search company down the road to make the most of it.
Ok, enough of the waffle, let’s get working.
Introducing hCard
You may have come across hCard. It’s a microformat for describing contact information (or really address book information) from within your HTML. It’s based on the vCard format, which is the format the contacts/address book program on your computer uses. All the usual fields are available – name, address, town, website, email, you name it.
If you’re running Firefox and Greasemonkey (or if you can, just to try this out), install this user script. What it does is look for instances of the hCard microformat in a page, and then add in a link to pass any hCards it finds to a web service which will convert it to a vCard. Take a look at the About the author box at the bottom of this article. It’s a hCard, so you should be able to click the icon the user script inserts and add me to your Outlook contacts or OS X Address Book with just a click.
So microformats are useful after all. Free microformats all round!
Implementing hCard
This is the really easy bit. All the hCard microformat is, is a bunch of predefined class names that you apply to the markup you’ve probably already got around your contact information. Let’s take the example of the About the author box from this article. Here’s how the markup looks without hCard:
<div class="bio">
<h3>About the author</h3>
<p>Drew McLellan is a web developer, author and no-good swindler from
just outside London, England. At the
<a href="http://www.webstandards.org/">Web Standards Project</a> he works
on press, strategy and tools. Drew keeps a
<a href="http://www.allinthehead.com/">personal weblog</a> covering web
development issues and themes.</p>
</div>
This is a really simple example because there’s only two key bits of address book information here:- my name and my website address. Let’s push it a little and say that the Web Standards Project is the organisation I work for – that gives us Name, Company and URL.
To kick off an hCard, you need a containing object with a class of vcard. The div I already have with a class of bio is perfect for this – all it needs to do is contain the rest of the contact information.
The next thing to identify is my name. hCard uses a class of fn (meaning Full Name) to identify a name. As is this case there’s no element surrounding my name, we can just use a span. These changes give us:
<div class="bio vcard">
<h3>About the author</h3>
<p><span class="fn">Drew McLellan</span> is a web developer...
The two remaining items are my URL and the organisation I belong to. The class names designated for those are url and org respectively. As both of those items are links in this case, I can apply the classes to those links. So here’s the finished hCard.
<div class="bio vcard">
<h3>About the author</h3>
<p><span class="fn">Drew McLellan</span> is a web developer, author and
no-good swindler from just outside London, England.
At the <a class="org" href="http://www.webstandards.org/">Web Standards Project</a>
he works on press, strategy and tools. Drew keeps a
<a class="url" href="http://www.allinthehead.com/">personal weblog</a> covering web
development issues and themes.</p>
</div>
OK, that was easy. By just applying a few easy class names to the HTML I was already publishing, I’ve implemented an hCard that right now anyone with Greasemonkey can click to add to their address book, that Google and Yahoo! and whoever else can index and work out important things like which websites are associated with my name if they so choose (and boy, will they so choose), and in the future who knows what. In terms of effort, practically nil.
Where next?
So that was a trivial example, but to be honest it doesn’t really get much more complex even with the most pernickety permutations. Because hCard is based on vCard (a mature and well thought-out standard), it’s all tried and tested. Here’s some good next steps.
Play with the hCard Creator
Take a deep breath and read the spec
Start implementing hCard as you go on your own projects – it takes very little time
hCard is just one of an ever-increasing number of microformats. If this tickled your fancy, I suggest subscribing to the microformats site in your RSS reader to keep in touch with new developments.
What’s the take-away?
The take-away is this. They may sound like just more Web 2-point-HoHoHo hype, but microformats are a well thought-out, and easy to implement way of adding greater depth to the information you publish online. They have some nice benefits right away – certainly at geek-level – but in the longer term they become much more significant. We’ve been at this long enough to know that the web has a long, long memory and that what you publish today will likely be around for years. But putting the extra depth of meaning into your documents now you can help guard that they’ll continue to be useful in the future, and not just a bunch of flat ASCII. |
2005 |
Drew McLellan |
drewmclellan |
2005-12-06T00:00:00+00:00 |
https://24ways.org/2005/practical-microformats-with-hcard/ |
code |