Accessing CSS class using javascript

Question

How can i access the style declaration of an element specified using external or embedded stylesheet.For ex: how to access the width property of an element which is defined in an embeded stylesheet using the id selector.. I know CSSRules object can do this...But it is browser dependent.For ex:in chrome ,the object is null...So what is the browser independent way to do this?

Answer 1

This is really browser dependent... I have a bit of code which I use to make an auto-expand text area, adapted from code found there.

Note, the $ function here is from Prototype.

function getStyleFromCss(el, style) {
    /* Hack required by IE */
    var value = $(el).getStyle(style);
    if (!value) {
        /* For other browsers. Actually this equals 'window'. Use that
         *  if Opera fails on you. */
        if(document.defaultView) {
            value = document.defaultView.getComputedStyle(el, null).
                getPropertyValue(style);
            // for IE
        } else if(el.currentStyle) {
            value = el.currentStyle[style];
        }
    }
    if(value.length > 0){
        /* if the value returned has the word px in it, we check for
         *  the letter x */
        if (value.charAt(value.length-1) == "x") {
            value = parseInt(value.substring(0, value.length-2));
        }
    }
    return value;
}

The getStyle() function from Prototype is defined this way, you should be able to easily adapt it to your needs.

getStyle: function(element, style) {
  element = $(element);
  style = style == 'float' ? 'cssFloat' : style.camelize();
  var value = element.style[style];
  if (!value || value == 'auto') {
    var css = document.defaultView.getComputedStyle(element, null);
    value = css ? css[style] : null;
  }
  if (style == 'opacity') return value ? parseFloat(value) : 1.0;
  return value == 'auto' ? null : value;
},