借助script发送http请求：jsonp

function getJSONP(url,callback){   var cbnum ='cb'+getJSONP.counter++;   var cbname = 'getJSONP.'+cbnum;   if(url.indexOf('?') === -1)   url += '?jsonp='+cbname;   else   url += '&jsonp='+cbname;   var script = document.createElement('script');   getJSONP[cbnum] = function(response){      try{         callback(response);      }      finally{         delete getJSONP[cbnum];//删除该函数         script.parentNode.removeChild(script);//移除script元素      }   };   //立即出发http请求   script.src = url;//设置脚本url   document.body.appendChild(script);}//当页面全部加载以后window.onload = function(){   getJSONP.counter = 0;   getJSONP('http://api.taobao.com/apitools/ajax_props.do',function(res){    alert(res);   });};