addClass, removeClass, toggleClass（从jquery中抠出来）

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

 var mylibs = (function(){
     var rtrim = /^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g,
         core_trim = String.prototype.trim,
         core_rspace = /\s+/,
         rclass = /[\t\r\n]/g;

     var trim = function(text){
         if(core_trim && !core_trim.call("\uFEFF\xA0")){
             return text == null ?
                 "" :
                 core_trim.call(text);
         }else{
             return text == null ?
                 "" :
                 (text + "").replace(rtrim, "");
         }
     };

     return {
         addClass:function(elem,value){
             var classNames,setClass;

             if (!value || typeof value !== "string") return;
             if (elem.nodeType !== 1) return;

             classNames = value.split(core_rspace);

             if (!elem.className && classNames.length === 1){
                 elem.className = value;
             }else{
                 setClass = " " + elem.className + " ";

                 for (var i = 0; i < classNames.length; i++){
                     if (setClass.indexOf(" " + classNames[ i ] + " ") < 0)
                         setClass += classNames[ i ] + " ";
                 }
                 elem.className = trim(setClass);
             }
         },
         removeClass:function(elem,value){

             var removes,className;

             if ((!value || typeof value !== "string") && value !== undefined) return;
             if (elem.nodeType !== 1 || !elem.className) return;

             removes = (value || "").split(core_rspace);
             className = (" " + elem.className + " ").replace(rclass," ");

             // loop over each item in the removal list
             for (var i=0;i<removes.length;i++){
                 // Remove until there is nothing to remove,
                 while (className.indexOf(" " + removes[i] + " ") >= 0)
                     className = className.replace(" " + removes[i] + " "," ");
             }
             elem.className = value ? trim(className) : "";
         },
         toggleClass:function(elem,value,stateVal){
             var type = typeof value,
                 isBool = typeof stateVal === "boolean";

             if (type !== "string") return;

             // toggle individual class names
             var className,
                 i = 0,
                 state = stateVal,
                 classNames = value.split(core_rspace);

             while ((className = classNames[ i++ ])){
                 // check each className given, space separated list
                 state = isBool ? state : !this.hasClass(elem,className);
                 (state ? this['addClass'] : this['removeClass'])(elem,className);
             }
         },
         hasClass:function(elem,selector){
             var className = " " + selector + " ";
             if (elem.nodeType === 1 && (" " + elem.className + " ").replace(rclass," ").indexOf(className) >= 0)
                 return true;
             return false;
         }
     };
 })();

 var dom = document.getElementById('d3');
 mylibs.addClass(dom,'red');
 mylibs.removeClass(dom,'cur');
 mylibs.toggleClass(dom,'red cur');