getClass兼容ie

if (!document.getElementsByClassName) {
	document.getElementsByClassName = function(className, element) {
		var children = (element || document).getElementsByTagName('*');
		var elements = new Array();
		for (var i = 0; i < children.length; i++) {
			var child = children[i];
			var classNames = child.className.split(' ');
			for (var j = 0; j < classNames.length; j++) {
				if (classNames[j] == className) {
					elements.push(child);
					break;
				}
			}
		}
		return elements;
	};
}