jquery 如何判断iframe是否加载完成

var iframe = document.createElement("iframe"); 

iframe.src = "http://www.baidu.com"; 

if (iframe.attachEvent){ 

    iframe.attachEvent("onload", function(){ // IE 

        alert("Local iframe is now loaded."); 

    }); 

} else { 

    iframe.onload = function(){ // 非IE 

        alert("Local iframe is now loaded."); 

    }; 

} 

document.body.appendChild(iframe);