getelement

//获取元素
var $ = {
  byId: function(id) {
		return typeof id == "string" ? document.geteleentById(id) : id;
	},
	byClass: function(cls, parent, tag) {
		var parent = parent || document;
		var tag = tag || "*";
		if(parent.geteleentsByClassName) {
			return parent.geteleentsByClassName(cls);
		} else {
			var aClass = [];
			var reg = new RegExp("(^| )" + cls + "( |$)");
			var aele = this.byTag(tag, parent);
			for(var i = 0, len = aele.length; i < len; i++) {
				reg.test(aele[i].className) && aClass.push(aele[i]);
			}
			return aClass;
		}
	},
	byTag: function(ele, obj) {
		return(obj || document).geteleentsByTagName(ele);
	}
}