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);
});
};