SetStyle: Set CSS Properties Without Surprises

Introduction

Using JavaScript to make HTML element, often is used elem.setAttribute("style", "property1:val; property2:val;") to set CSS properties in easy way; but there's a problem if you had just set a CSS property with elem.style.prop="val" : it will be reset to default browser value!! (Run the test code showed below.)

So I made a simple function to solve this problem and continue to use a setAttribute-like approach.

Using the Code

I wrote the setStyle method in HTMLElement interface, that represents any HTML element, so to use it easily.

This is the function:

HTMLElement.prototype.setStyle = function(str) {    
    var props = str.split(";"); //get properties
    for(var i = 0; i < props.length; i++) {
        var t = props[i].split(":"); //t[0] = property - t[1] = value
        this.style[fixPropName(t[0].trim())] = t[1].trim(); //trim removes white space(s)
    }
}

String.prototype.capitalize = function() {
    return this.charAt(0).toUpperCase() + this.slice(1);
}

//transform text, for example, from background-color to backgroundColor
function fixPropName(str) {
    var tArray = str.split("-");
    var prop = tArray[0];
    for(var i = 1; i < tArray.length; i++) {
        prop += tArray[i].capitalize();
    }
    return prop
}

Now you can use this function, in this way:

var div = document.getElementById("IdElement");
div.setStyle("background:blue; color: white"); 

This function is just a millisecond (on my PC, and sometimes) slower than setAttribute method, but now you are sure to haven't unexpected CSS properties change.

To make a test, run this code:

<script>
HTMLElement.prototype.setStyle = function(str) {    
    var props = str.split(";"); //get properties
    for(var i = 0; i < props.length; i++) {
        var t = props[i].split(":"); //t[0] = property - t[1] = value
        this.style[fixPropName(t[0].trim())] = t[1].trim(); //trim removes white space(s)
    }
}

String.prototype.capitalize = function() {
    return this.charAt(0).toUpperCase() + this.slice(1);
}

function fixPropName(str) {
    var tArray = str.split("-");
    var prop = tArray[0];
    for(var i = 1; i < tArray.length; i++) {
        prop += tArray[i].capitalize();
    }
    return prop
}

window.addEventListener("DOMContentLoaded", 
function(e) {

var div = document.getElementById("cc");
div.style.opacity = "1";
str = "Opacity: " + div.style.opacity + "
";
var endTime, startTime = Date.now(); 
div.setAttribute("style","background:green;color:black");
endTime = Date.now(); 
str += "TimeExec: " +(startTime-endTime) + "
";
str += "Opacity: " + div.style.opacity + "

";

div.style.opacity = "1";
str += "Opacity: " + div.style.opacity + "
";
startTime = Date.now(); 
div.setStyle("background:blue; color: white");
endTime = Date.now(); 
str += "TimeExec: " +(endTime-startTime) + "
";
str += "Opacity: " + div.style.opacity + "
";

div.innerHTML = str;
}, false);
</script>

To to to

Updates 

31/01/2014: Added fixPropName function to transform property text from, for example, background-color to backgroundColor