判断 iframe 是否加载完成的完美方法

var iframe = document.createElement("iframe");
iframe.src = "http://www.google.com.hk";

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);