延迟加载JavaScript

 1 function downloadJSAtOnload() {
 2     var element = document.createElement("script");
 3     element.src = "defer.js";
 4     document.body.appendChild(element);
 5 }
 6 if (window.addEventListener)
 7     window.addEventListener("load", downloadJSAtOnload, false);
 8 else if (window.attachEvent)
 9     window.attachEvent("onload", downloadJSAtOnload);
10 else window.onload = downloadJSAtOnload;