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Setting CSS3 properties using JavaScript

Last Updated: April 9th, 2013

Setting CSS properties using JavaScript is nothing new, and for the most part follows a very predictable path:

document.getElementById("adiv").style.height="100px" //set CSS height property using JavaScript
document.body.style.backgroundColor="yellow" //set CSS background-color property using JavaScript

You'd first access the "style" object of an element, then follow it up with the desired CSS property name to set it. If the CSS property name is hyphenated, such as "background-color", drop the hyphen and capitalize the character following it when referring to it in JavaScript. Simple enough right? With setting CSS3 properties, technically nothing changes; the problem is knowing which property to set! You see, as browsers raced to support CSS3 properties before they're finalized, the use of vendor prefixes was what the browsers turned to offer an "interim" solution while the details of the official properties are hashed out . All major browsers have their own vendor prefix, which are:

For example, to add a CSS3 box shadow (box-shadow property) to an element at the moment, you need to define 3 separate CSS properties to cover all your bases (IE9+, FF3.5+, Safari 4+/Chrome and Opera 8.5+):

#mydiv{
box-shadow: 7px 7px 8px #818181;
-webkit-box-shadow: 7px 7px 8px #818181;
-moz-box-shadow: 7px 7px 8px #818181;
}

Setting CSS vendor properties in CSS is mostly just an exercise in patience, but when it comes to JavaScript, you can add logistics to it as well. While the normal rules of setting CSS using JavaScript still apply for setting vendor specific CSS properties, how do we know which property to set? For example, in FF3.5, -moz-box-shadow is the supported property, while in IE9, it's the official box-shadow property that it recognizes instead. Sure we can just set all of the possible properties, but the question is, would you still respect yourself as a coder at the end of the day if you did that? A more efficient, elegant way is to probe the browser to see which CSS property it supports, then set that property only.

Setting CSS3 properties in JavaScript

So how exactly can we go about setting a CSS3 property when different browsers may support a different variation of the property? The key lies in the fact that if a browser supports a particular CSS property, it will return a string value (empty string if not set yet) when you request it from an element on the page. In other words, the property exists on the element. If it doesn't, the value undefined is returned instead. With that in mind, we can perform a one-time check before setting a CSS3 property which variant of the property it supports, and always turn to that one in our code. With that said, lets construct a function that accepts an array of CSS properties and returns the one the browser supports as a string:

function getsupportedprop(proparray){
	var root=document.documentElement //reference root element of document
	for (var i=0; i<proparray.length; i++){ //loop through possible properties
		if (proparray[i] in root.style){ //if property exists on element (value will be string, empty string if not set)
			return proparray[i] //return that string
		}
	}
}

//SAMPLE USAGE
var boxshadowprop=getsupportedprop(['boxShadow', 'MozBoxShadow', 'WebkitBoxShadow']) //get appropriate CSS3 box-shadow property
document.getElementById("mydiv").style[boxshadowprop]="5px 5px 1px #818181" //set CSS shadow for "mydiv"

The below makes use of the getsupportedprop() function to see which CSS box-shadow property your browser supports- "boxShadow", "MozBoxShadow", or "WebKitBoxShadow" when the button is clicked on:

function alertboxshadow(){
	alert(getsupportedprop(['boxShadow', 'MozBoxShadow', 'WebkitBoxShadow']))
}

If you're using FF3+, you should get "MozBoxShadow", in IE9+ and Opera9+, "boxShadow", and in Safari4+ and Chrome, "WebKitBoxShadow". In other browsers, the value undefined should be returned.

Armed with the above function, we can now go about setting CSS3 properties in JavaScript more easily, by passing into the function a list of possible variants of a particular CSS3 property, and letting the function figure out which one the browser supports and should be adopted. To drive this point home, lets set up a demo where 3 different CSS3 properties can be dynamically added or removed to a link button with relative ease, thanks to the aforementioned function:

<script>
var shadowprop=getsupportedprop(['boxShadow', 'MozBoxShadow', 'WebkitBoxShadow'])
var roundborderprop=getsupportedprop(['borderRadius', 'MozBorderRadius', 'WebkitBorderRadius'])
var csstransform=getsupportedprop(['transform', 'MozTransform', 'WebkitTransform', 'msTransform', 'OTransform'])

function changecssproperty(target, prop, value, action){
	if (typeof prop!="undefined")
		target.style[prop]=(action=="remove")? "" : value
}
</script>

<body>

<a id="cfbutton" href="http://www.codingforums.com">Coding Forums</a>

<script>
var z=document.getElementById("cfbutton")
</script>

<a href="javascript:changecssproperty(z, shadowprop, '6px 6px 8px rgba(0,0,0,.5)')">Add Shadow</a> 
<a href="javascript:changecssproperty(z, shadowprop, '', 'remove')">Remove Shadow</a>

<a href="javascript:changecssproperty(z, roundborderprop, '15px')">Add Round Border</a> 
<a href="javascript:changecssproperty(z, roundborderprop, '', 'remove')">Remove Round Border</a>

<a href="javascript:changecssproperty(z, csstransform, 'rotate(25deg)')">Add Transform Rotate</a> 
<a href="javascript:changecssproperty(z, csstransform, '', 'remove')">Remove Transform</a>

Demo:

Coding Forums

As you can see, we first use the getsupportedprop() function to get and cache each variant of CSS3's box-shadow, border-radius, and transform properties the browser supports. Then, using these properties, we go about manipulating them dynamically in JavaScript.

Moving on, the getsupportedprop() above, while does get the job done, frankly could use some refactoring to be more elegant and versatile. That's what we'll aim to do next.

• Setting CSS3 properties using JavaScript
• Creating a generic CSS3 property retriever function

Creating a generic CSS3 property retriever function