getComputedStyle Polyfill

getComputedStyle.js

if (!window.getComputedStyle) {
    /**
     * @param {(Element|null)} e
     * @param {(null|string)=} t
     * @return {(CSSStyleDeclaration|null)}
     */
    window.getComputedStyle = function(e, t) {
        return this.el = e, this.getPropertyValue = function(t) {
            /** @type {RegExp} */
            var n = /(\-([a-z]){1})/g;
            return t == "float" && (t = "styleFloat"), n.test(t) && (t = t.replace(n, function() {
                return arguments[2].toUpperCase();
            })), e.currentStyle[t] ? e.currentStyle[t] : null;
        }, this;
    };
}

// EXAMPLE
// Reference: http://snipplr.com/view/13523/
window.onload = function() {
  var compStyle = window.getComputedStyle(document.getElementById('test'), "");
  alert(compStyle.getPropertyValue("color"));
  alert(compStyle.getPropertyValue("float"));
  alert(compStyle.getPropertyValue("background-color"));
}

thanks bro