Category Archives: JavaScript

jQuery plugin to associate label “for” attribute with form controls that have dynamic id’s

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For whatever reason, you can’t associate your labels with your form controls implicitly by wrapping both the label text and the control in a <label> element:

<label>
  Email address: <input type="email" name="email" value="" placeholder="you@example.com"/>
</label>

You’ve had to explicitly state the form control you want the label to be associated with:

<label for="email">Email address:</label>
<input id="email" type="email" name="email" value="" placeholder="you@example.com"/>

…but your framework has other ideas, it decides to commandeer your precious “id” attribute and change it from a simple and beautiful “email” into a junky “dnn_ctr1163_RegistrationForm_email”. *cough* DotNetNuke *cough*, but also *cough* Wicket *cough* and probably a whole load of others.

The problem is now that your label is no longer associated with your form control, and there isn’t a simple fix, like, for example, change the for attribute to read “dnn_ctr1163_RegistrationForm_email”, because the numbers in the id change each time you refresh the page. The ID is dynamic, and you are receiving accessibility black stars.

So, luckily I noticed that often the id will change, but the framework will leave your originally intended id somewhere in there. I’ve written a jQuery plugin to look at label for attributes and try to find the form control you intended to associate it with before your server side framework so rudely changed it.

How to use

  1. Download the plugin and add it to your page
  2. Select the labels you want to re-associate and call the function eg. $(‘label’).fuzzyFor();

TODO

The plugin finds matches by looking for input, select and textarea elements in the document and checking to see if the for attribute in your label element appears in the id attribute of the form control. At the moment if more than one match is found, it just uses the first (which is probably good enough for most). However, it should probably do something a bit more clever and use the form control that is closest to the label (I’m reasoning that you normally put your label’s close to your controls).

Array.toString

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I was recently trying to debug some code that returned an array of arrays. In Actionscript and seemingly most (if not all) ECMAScript implementations, when calling toString on an array object it passes back a comma separated list of elements in the array. This is no good if you have nested arrays because:

    [1, 2, 3, [1, 2, 3]].toString();

…returns:

    "1, 2, 3, 1, 2, 3"

So it appears as a flat array, whereas the underlying object is something entirely different. So if you happen to be quickly debugging using trace (ActionScript) or alert (JavaScript) the object can appear to be something it is not.

If you want the Array object to return a string of comma separated elements contained in square braces then run this snippet somewhere before you start creating new Array objects:

    Array.prototype._toString = Array.prototype.toString;
    Array.prototype.toString = function() {return '[' + this._toString() + ']';}

Now:

    [1, 2, 3, [1, 2, 3]].toString();

…returns:

    "[1, 2, 3, [1, 2, 3]]"

Much better!

jQuery plugin to add a CSS class to last-child DOM elements

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This has been bugging me for ages. IE < 9 does not support the CSS3 last-child pseudo class. I’ve created a _very_ simple jQuery plugin to add a CSS class “last-child” to the element that is the last child of a DOM element.

It performs this recursively, so it’ll apply the class to the last child of an element as well as to the last child of all it’s children…and so on and so forth.

It’ll perform this on each of the set of matched elements in a jQuery object. So you can have it traverse the whole, of your page by providing a jQuery object with the <body> element in it, or you can pick and choose DOM elements to apply the plugin to for efficiency. For instance, you might only need the "last-child" class to be applied to the last child of an unordered or ordered list:

    $('body').lastChild(); // Applies to all elements attached to the document.body
    $('ul, ol').lastChild(); // Applies to all elements in an unordered or ordered list

By default, the plugin applies the CSS class to a restricted set of DOM element types. You can specify the types of DOM elements to apply the class to by passing an options object to the function. In this way you can also specify the name of the CSS class that will be applied:

    $('ul, ol').lastChild({
        tags:['li'], // Only elements with the tag name 'li' will have the class applied to them
        cssClass:'ie-last-child' // The CSS class name will be 'ie-last-child'
    });

For super shorthand, you can simply pass a string to the lastChild function – which it presumes to be the CSS class you want to use:

    $('ul, ol').lastChild('ie-last-child');

You can download the plugin here.

Note, while I created this plugin to get around my IE problem, it is not built specifically for IE. If you only want IE to receive these classes, you’ll probably want to do something like:

    if($.browser.msie) {
        $('body').lastChild();
    }

…but obviously preferably using Modernizr:

    if($('.ie6, .ie7, .ie8').length) {
        $('body').lastChild();
    }

Enjoy!

Modernizr progressives or exceptions?

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Modernizr, what an interesting tool you are. How do I use your class names in my CSS files? You’ve given me a choice and I’m not sure what to use:

.multiplebgs div p {
  /* properties for browsers that
     support multiple backgrounds */
}
.no-multiplebgs div p {
  /* optional fallback properties
     for browsers that don't */
}

There are two ways to view this, bottom up, and top down. They both have their advantages and disadvantages, and I’m going to attempt to highlight these for you, so you can make your own decision.

Bottom up

For the “bottom up” way of doing things, we define a lowest common denominator. A set of styles that will work with all the browsers your website is designed to target. The intersection of all the features of all your browsers, if you want to put it that way. From here, we use Modernizr to progressively enhance the user’s browsing experience for browsers that support particular features. An example may help:

a.btn {
  background:transparent url(../img/btn-red.gif) no-repeat scroll 0 0;
  padding:5px;
  display:inline-block;
  width:40px;
}
.borderradius a.btn {
  background-color:red;
  background-image:none;
  border-radius:5px;
}

The advantages being:

  • A clearly defined baseline that works on all browsers we’re coding for
  • If we aren’t able to determine client features (because for example, Modernizr is not available: the CDN is down, or the client doesn’t have JavaScript enabled) we know that the baseline styles will be used and will ensure the site looks acceptable regardless

The disadvantages are:

  • We end up writing more and more CSS as we utilise new features that become available
  • It doesn’t encourage a particularly forward thinking coding practice. You’re essentially coding for the browser with the lowest feature set
  • If you want to change the baseline styles because of a redesign or perhaps your baseline is raised, you’re probably going to have to change overridden styles in the progressive enhancement style blocks as well

Top down

The “top down” approach is where we define styles for new browsers, and then use the “no-” prefix classes to define exceptions for browsers that don’t support the feature we’re exploiting. e.g.

a.btn {
  border-radius:5px;
  background-color:red;
  padding:5px;
  display:inline-block;
  width:40px;
}
.no-borderradius a.btn {
  background:transparent url(../img/btn-red.gif) no-repeat scroll 0 0;
}

We’re forward thinking, assuming everyone viewing our site is using these great new features and coding in fallbacks for the exceptions to the rule. Our view is that one day, all browsers will support the styles we’re using…and we’re adding in exceptions for in the mean time. The advantages are:

  • We end up writing less CSS, as we don’t have to override properties we’ve previously declared that the browser doesn’t understand
  • Our mindset is altered slightly, encouraging us to make use of and exploit new browser features that allow us to code and prototype faster
  • As our browser baseline increases, it’s really easy to remove exceptions that are no longer used

The disadvantages are:

  • We’re totally relying on Modernizr and the browser having JavaScript enabled. Without JavaScript the “no-” prefixed classes are not added to the <html> element and the browser is left trying to style things that aren’t supported or use style declarations that don’t exist (as far as the browser knows).

Well, sort of. You could always use the “no-js” class on the <html> element which Modernizr normally removes and replaces with “js” (to indicate JavaScript is available). You’d define your styles as above, but then define a lowest common denominator style set, for when you don’t know what features a browser does or doesn’t support. That’s kind of overkill though.

So, that’s basically it. When I first thought about it my gut reaction was to sit in the bottom up camp, but after thinking about it, and considering the audience for the project I’m working on it makes more sense to use the top down approach. Especially now that I’ve written it down like this. I’m hoping it’ll help others to make the right decision.

Highlight text using jQuery and the HTML5 mark tag

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Here’s a jQuery plugin I wrote that’ll add HTML5 <mark> tags around keywords or phrases in an element’s body text.

What is mark?

a run of text in one document marked or highlighted for reference purposes, due to its relevance in another context

http://www.whatwg.org/specs/web-apps/

Usage

Add the script to your page, and then when the DOM is ready, do something like:

    $('body').mark('Lorem ipsum');

The plugin can actually be used to wrap any tag around keywords. Simply pass the tag name you want to use as an option:

    $('body').mark({
      text: 'Lorem ipsum',
      tag:  'span',
      cssClass:  'mark'
    });

The above example will wrap span elements around the words lorem and ipsum. Each span element will have the class ‘mark’. View an example implementation.

TODO

  1. Input sanitation on the text to be marked. Currently the text is dumped straight into a regular expression. It needs to be escaped so that any regular expression meta-characters are interpreted as literals.
  2. Similarly, HTML special characters in the input need to be expanded into their HTML entities.
  3. From what I can see, IE doesn’t like <mark> tags, and seems to automatically self close the opening and closing tags inserted into the DOM. WTF? Can anyone shed any light on this problem? For now, you’re going to have to use a <span> with a CSS class

If you’re interested in contributing, get in touch

iframe automatic height adjustment using HTML5 cross domain web messaging

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Yesterday I was working on a site that needed an iframe embedded in the page whose content came from a completely different domain. I try to steer clear of iframes at all costs normally so forgive me if what I’m about to say is pretty obvious.

I didn’t want the content in the iframe to appear as though it was in an iframe, so obviously I stripped off all the default browser styles…well, the border. I wanted the iframe to be as high as the content it was containing so that no scroll bars would appear.

So what I did was just give the iframe a height, however when the user navigated to a different page within the iframe, the height I had previously set was too big or too small.

I instantly thought “right, JavaScript will sort this out for me!” and proceeded to quickly code up a function that would inspect the scrollHeight of the content in the iframe and adjust the iframe height accordingly.

No! Said cross domain policy. I had momentarily forgotten all about that. Since the iframe content came from a different domain, I wasn’t allowed to access the document object of the iframe (or vice versa).

Here is how not to do it

Firefox says “Error: Permission denied to access property ‘document’” and other browsers similar.

I started searching for some kind of workaround.  Of course there isn’t really one…except I did find an interesting hack for Firefox. Which is – an iframe document can alter the url fragment of the parent window’s location object! ha madness.

The idea is that the document in the iframe alters the url fragment to read:

http://freestyle-developments.co.uk/blog/?p=150#138

Where 138 is the height of the iframe document (obviously you could be a bit more fancy and send other parameters and name them e.g #height:138 but for simplicity I’ve just set the value). The parent then reads this value and sets the iframe height accordingly:

var iFrameHeight = parseInt(location.hash.replace('#', ''));

So…yeah, that’s pretty interesting, but not really a solution. Check out the example implementation here.

Anyway, what to do? HTML5 web messaging to the rescue! Sweet! HTML5 web messaging is cross domain messaging done right. Not only does the messenger choose who should receive messages, but the recipient also chooses who to receive messages from.

The idea is that after the iframe document has loaded, it sends a message to the parent window telling it what it’s scrollHeight is. The parent listens for messages, and sets the height of the iframe when it receives a message.

A couple of things to note:

  1. There has to be communication between the two documents. i.e. the document on the external domain needs to actively send this message. Which can be a complete show stopper if you have no control over the document on the external domain
  2. This isn’t going to work on IE < 9. I tested the implementation linked below is working on FireFox 4 (Beta 7), Safari 5.0.2, Chrome 8, Opera 10.63 and Internet Explorer 9 Platform Preview 7. Which is a pretty good spread to be honest

Check out the example HTML5 web messaging implementation here.

Update: Hardware accelerated alternative to jQuery animate() top, left, width, height and opacity CSS properties for iPhone/iPad

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Update to my post here – I’ve tweaked the script to use CSS3 transitions on Firefox 4+ and Opera 10.50+ as well as modern webkit based browsers such as Chrome and Safari.

The CSS3 transforms and transitions enhanced carousel can be found here:
freestyle-developments.co.uk/demo/public/portsurf/?css3

…and the normal carousel:
freestyle-developments.co.uk/demo/public/portsurf/

Source code for CSS3 transforms and transitions enhanced carousel

N.B. The normal carousel works in IE7 and IE9 beta, but not in IE8 (it seems IE8 can’t figure out the dimensions of DOM elements properly).

Hardware accelerated alternative to jQuery animate() top, left, width, height and opacity CSS properties for iPhone/iPad

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I was recently asked to quote for a proof of concept HTML5 alternative to a flash carousel, specifically to run on iPad. I said I’d do it, but the agency later decided that others had tried to create a HTML5 version and had not been able to create a version that performed well enough for the client. From my point of view they were under the impression I couldn’t do any better. So naturally, I spent a few hours of my spare time proving this wrong, just for the fun of it.

Step 1 was to build a version of the carousel in HTML5. I chose to use the jQuery framework because…well, I felt like it. The fruits of my labour are here:

http://freestyle-developments.co.uk/demo/public/portsurf/

Now, you can view this on any browser. All that is happening is that there are a set of list items absolutely positioned in a container, when you click/touch an item on the left/right jQuery animates the top, left, width, height and opacity CSS values for each item.

Fantastic, but, it feels really sluggish on iPad and iPhone 4. Go on, try it out.

Fair enough, they are resource constrained devices. What to do though? I’ve already used all the tricks I could think of fast loops, select operation caching etc. etc. So what now?

Luckily, in iOS, transitions and animations of the -webkit-transform and opacity properties are performance-enhanced. Sweet! These correspond exactly to the two CSS properties I’m trying to manipulate for each item in my carousel. Implementation was a simple case of swapping out the jQuery animate function, for the css function. Passing in the webkit transition, webkit transform and opacity values in its place.

For example:

items[itemIndex - 3].css({
	opacity:1,
	'-webkit-transform':'translate3d(' + carousel.itemPosition.medium.left.x 
            + 'px, ' + carousel.itemPosition.medium.left.y + 'px, 0) scale(0.5)',
	'-webkit-transition':'opacity 0.4s linear, -webkit-transform 0.4s linear'
});

The webkit transition property is saying “transition these CSS properties from what they were previously to their new values, using these transition parameters (0.4s linear)”. The webkit transform property is saying “move this element to the following coordinates, and scale it by a factor of 0.5″.

Check out the hardware accelerated version on your iPad/iPhone and compare it with the other:

http://freestyle-developments.co.uk/demo/public/portsurf/?ha=1 (Note: webkit only)

Here is a video demonstrating the performance differences those of you without iPads.

JavaScript Namespace

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I normally put my JavaScript function/classes/other things in namespaces. Namespacing your JavaScript is good, it avoids conflicts between scripts on the page and keeps the global namespace clean. I could go into more detail, but luckily it has been done for me.

Declaring namespaces, and checking they exist before using them is a bit of a pain. You might find yourself doing something like:

if(!window.com) window.com = {};
if(!com.mycompany) com.mycompany = {};
if(!com.mycompany.mypackage) com.mycompany.mypackage = {};

…and then add things to it like:

com.mycompany.mypackage.myfunction = function() { return 138; };

To make things worse, if your webpage includes a different script that uses slightly different namespace, say "com.mycompany.mypackage2" you’ll have to check again that the objects "com" and "com.mycompany" already exist.

The following function allows you to use a namespace, without having to manually go through the throws of checking each "space" exists and creating an empty object for each level.

/**
 * I declare a namespace if it doesn't already exist.
 *
 * @param {String} ns The namespace to create/use
 * @param {Object} parent (Optional) The parent object onto which this namespace will be attached.
 * @return True if the namespace was created successfully.
 * @type Boolean
 */
function namespace(ns, parent) {

	if(!parent) {
		parent = window;
	} else {
		// Parent must be an object
		if(typeof(parent) != 'object') {
			return false;
		}
	}

	var names = ns.split('.');

	if(!names.length) {
		return true;
	}

	var name = names[0];

	if(!parent[name]) {
		parent[name] = {};
	}

	if(names.length > 1) {
		names.shift();
		return namespace(names.join('.'), parent[name]);
	}

	return true;
}

…and is used like so:

namespace('com.mycompany.mypackage');
com.mycompany.mypackage.myfunction = function() { return 138; };