javascript中的一个兼容类

在看javascript高级程序设计的时候记录下来的

var EventUtil={
          addHandler:function(element,type,handler){
               if(element.addEventListener)
                    element.addEventListener(type,handler,false);
               else if(element.attachEvent)
                    element.attachEvent("on"+type,handler);
               else
                    element["on"+type]=handler;
          },
          removeHandler:function(){
               if(element.removeEventListener)
                    element.removeEventListener(type,handler);
               else if(element.detachEvent)
                    element.detach("on"+type,handler);
               else
                    element['on'+type]=null;
          },
          getEvent:function(event){
               return event ? event : window.event;
          },
          getTarget:function(event){
               return event.target ? event.target : event:srcElement;
          },
          preventDefault:function(event){
               if(event.preventDefault){
                    event.preventDefault();
               }
               else
                    event.returnVale=false;
          },
          stopPropagation:function(event){
               if(event.stopPropagation){
                    event.stopPropagation();
               }
               else
                    event.cancelBubble=true;
          },
          gettoElement:function(event){
               return event.relatedTarget || event.toElement;
          },
          getfromElement:function(event){
               return event.relatedTarget || event.fromElement;
          },
          getPageWidth:function(){
              var width=window.innerWidth;//兼容IE8
              if(typeof width != "number")
             {
                 if(document.compatMode=="CSS1Compat")
                 {
                      return document.documentElement.clientWidth;
                 }
                 else
                      return document.body.clientWidth;
             }
              return width;
         },
    getPageHeight:function(){
        var height=window.innerHeight;
        if(typeof height != "number")
        {
            if(document.compatMode=="CSS1Compat")
                return document.documentElement.clientHeight;
            else
                return document.body.clientHeight;
        }
        return height;
    }
     };
function createXHR(){
     if(typeof XMLHttpRequest !="undefined")
     {
          return new XMLHttpRequest();
     }
     else if(typeof ActiveXObject !="undefined")
     {
          if(typeof arguments.callee.activeXString !="string")
          {
               var versions=["MSXML2.XMLHTTP.6.0",
                    "MSXML2.XMLHTTP.3.0","MSXML2.XMLHTTP"],i,length;
               for(i=0;i<length;i++)
               {
                    try{
                         new ActiveXObject(versions[i]);
                         arguments.callee.activeXString=versions[i];
                         break;
                    }catch(e){
                    }
               }
          }
          return new ActiveXObject(arguments.callee.activeXString);
     }
     else{ 
          throw new Error("NO XHR object available.");
     }
}