// Implementation of the missing (nonexistant) 'document.getElementsByClassName()
document.getElementsByClassName = function(cl) {
	var retnode = [];
	var myclass = new RegExp('\\b'+cl+'\\b');
	var elem = this.getElementsByTagName('*');
	for (var i = 0; i < elem.length; i++) {
		var classes = elem[i].className;
		if (myclass.test(classes)) retnode.push(elem[i]);
	}
return retnode;
};

/**
 * call just like document.getElementById('') or document.getElementsByTagName('')
 */

getElementsByClassName

JavaScript