How to dynamically create CSS class in JavaScript and apply?

Question

I need to create a CSS stylesheet class dynamically in JavaScript and assign it to some HTML elements like - div, table, span, tr, etc and to some controls like asp:Textbox,

Answer 1

Short answer, this is compatible "on all browsers" (specifically, IE8/7):

function createClass(name,rules){
    var style = document.createElement('style');
    style.type = 'text/css';
    document.getElementsByTagName('head')[0].appendChild(style);
    if(!(style.sheet||{}).insertRule) 
        (style.styleSheet || style.sheet).addRule(name, rules);
    else
        style.sheet.insertRule(name+"{"+rules+"}",0);
}
createClass('.whatever',"background-color: green;");

And this final bit applies the class to an element:

function applyClass(name,element,doRemove){
    if(typeof element.valueOf() == "string"){
        element = document.getElementById(element);
    }
    if(!element) return;
    if(doRemove){
        element.className = element.className.replace(new RegExp("\\b" + name + "\\b","g"));
    }else{      
        element.className = element.className + " " + name;
    }
}

Here's a little test page as well: https://gist.github.com/shadybones/9816763

The key little bit is the fact that style elements have a "styleSheet"/"sheet" property which you can use to to add/remove rules on.