通过id TagName className 获取

/*-------------------------- +
获取id, class, tagName
+-------------------------- */
var get = {
byId: function(id) {
return typeof id === "string" ? document.getElementById(id) : id
},
byClass: function(sClass, oParent) {
var aClass = [];
var reClass = new RegExp("(^| )" + sClass + "( |$)");
var aElem = this.byTagName("*", oParent);
for (var i = 0; i < aElem.length; i++) reClass.test(aElem[i].className) && aClass.push(aElem[i]);
return aClass
},
byTagName: function(elem, obj) {
return (obj || document).getElementsByTagName(elem)
}
};

//例子：
//获取id：var oMsgBox = get.byId("msgBox");
//获取class：var aA = get.byClass("del", oUl)[0];
//获取tagname：var aLi = get.byTagName("li", oList)[0];