addClass方法（从jquery中抠出来）

<div id="d3" class="ghy"></div>

 1 var addClass = function(elem,value){
 2     var core_rspace = /\s+/,
 3         classNames = value.split(core_rspace),
 4         setClass;
 5         
 6     if (!value || typeof value !== "string") return;
 7     if (elem.nodeType !== 1) return;
 8         
 9     if (!elem.className && classNames.length === 1){
10         elem.className = value;
11     }else{
12         setClass = " " + elem.className + " ";
13         
14         for (var i = 0; i < classNames.length; i++){
15             if (setClass.indexOf(" " + classNames[ i ] + " ") < 0)
16                 setClass += classNames[ i ] + " ";
17         }
18         elem.className = trim(setClass);
19     }
20     
21     function trim(text){
22         var rtrim = /^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g,
23             core_trim = String.prototype.trim;
24         
25         if(core_trim && !core_trim.call("\uFEFF\xA0")){
26             return text == null ?
27                 "" :
28                 core_trim.call(text);
29         }else{
30             return text == null ?
31                 "" :
32                 (text + "").replace(rtrim, "");
33         }
34     };
35 };
36 
37 var dom = document.getElementById(‘d3‘);
38 addClass(dom,‘cur ghy‘);