getElementsByClassName polyfill

getElementsByClassName.js

/**
 * This polyfill is originally a part of: http://github.com/murger/Qj/
 * MIT license (http://opensource.org/licenses/mit-license.php)
 * usage: getElementsByClassName.call(document, 'awesome')
 */

var getElementsByClassName = (function () {
	if (typeof document.getElementsByClassName === 'function') {
		return document.getElementsByClassName;
	}

	return function (cssClass) {
		var nodes = (this === document)
				? document.body.children
				: this.children,
			push = Array.prototype.push,
			result = [],
			i = 0, j = 0,
			n, c,

			elHasClass = function (node) {
				return !!~(' ' + node.className + ' ').indexOf(' ' + cssClass + ' ');
			},

			hasChildren = function (node) {
				return (node.children && node.children.length);
			},

			filterNodeByClass = function (node) {
				if (elHasClass(node)) {
					push.call(result, node);
				}
			};

		while (n = nodes[i++]) {
			filterNodeByClass(n);

			if (hasChildren(n)) {
				j = 0;

				while (c = n.children[j++]) {
					if (hasChildren(c)) {
						push.call(nodes, c);
					} else {
						filterNodeByClass(c);
					}
				}
			}
		}

		return result;
	};
})();