判断 iframe 是否加载完成的完美方法

frome http://www.planabc.net/2009/09/22/iframe_onload/

var iframe = document.createElement("iframe");
iframe.src ="http://www.planabc.net";

if(iframe.attachEvent){
iframe.attachEvent("onload",function(){
alert("Local iframe is now loaded.");
});
}else{
iframe.onload =function(){
alert("Local iframe is now loaded.");
};
}

document.body.appendChild(iframe);