在没有为您提供所有跨浏览器兼容性的框架的情况下，最简单的操作就是将调用代码放在正文末尾。它比onload处理程序执行起来更快，因为它仅等待DOM准备就绪，而不等待所有图像加载。而且，这适用于所有浏览器。
<!doctype html>
<html>
<head>
</head>
<body>
Your HTML here
<script>
// self executing function here
(function() {
// your page initialization code here
// the DOM will be available here
})();
</script>
</body>
</html>
对于现代浏览器（来自IE9和更高版本以及任何版本的Chrome，Firefox或Safari），如果您希望能够实现类似jQuery的$(document).ready()方法，可以从任何地方调用（而不必担心调用脚本的位置），您可以只使用以下内容：
function docReady(fn) {
// see if DOM is already available
if (document.readyState === "complete" || document.readyState === "interactive") {
// call on next available tick
setTimeout(fn, 1);
} else {
document.addEventListener("DOMContentLoaded", fn);
}
}
用法：
docReady(function() {
// DOM is loaded and ready for manipulation here
});
如果您需要完全的跨浏览器兼容性（包括IE的旧版本）并且不想等待window.onload，那么您可能应该看看jQuery之类的框架如何实现其$(document).ready()方法。根据浏览器的功能，它相当复杂。
让您稍微了解一下jQuery的功能（无论放置script标记的位置都可以使用jQuery）。
如果支持，它将尝试标准：
document.addEventListener('DOMContentLoaded', fn, false);
后退到：
window.addEventListener('load', fn, false )
或对于较旧版本的IE，它使用：
document.attachEvent("onreadystatechange", fn);
后退到：
window.attachEvent("onload", fn);
而且，我不太了解IE代码路径中的一些变通办法，但看起来它与框架有关。
这是.ready()用普通javascript编写的jQuery的完全替代：
(function(funcName, baSEObj) {
// The public function name defaults to window.docReady
// but you can pass in your own object and own function name and those will be used
// if you want to put them in a different namespace
funcName = funcName || "docReady";
baSEObj = baSEObj || window;
var readyList = [];
var readyFired = false;
var readyEventHandlersInstalled = false;
// call this when the document is ready
// this function protects itself against being called more than once
function ready() {
if (!readyFired) {
// this must be set to true before we start calling callbacks
readyFired = true;
for (var i = 0; i < readyList.length; i++) {
// if a callback here happens to add new ready handlers,
// the docReady() function will see that it already fired
// and will schedule the callback to run right after
// this event loop finishes so all handlers will still execute
// in order and no new ones will be added to the readyList
// while we are processing the list
readyList[i].fn.call(window, readyList[i].ctx);
}
// allow any closures held by these functions to free
readyList = [];
}
}
function readyStateChange() {
if ( document.readyState === "complete" ) {
ready();
}
}
// This is the one public interface
// docReady(fn, context);
// the context argument is optional - if present, it will be passed
// as an argument to the callback
baSEObj[funcName] = function(callback, context) {
if (typeof callback !== "function") {
throw new TypeError("callback for docReady(fn) must be a function");
}
// if ready has already fired, then just schedule the callback
// to fire asynchronously, but right away
if (readyFired) {
setTimeout(function() {callback(context);}, 1);
return;
} else {
// add the function and context to the list
readyList.push({fn: callback, ctx: context});
}
// if document already ready to go, schedule the ready function to run
if (document.readyState === "complete") {
setTimeout(ready, 1);
} else if (!readyEventHandlersInstalled) {
// otherwise if we don't have event handlers installed, install them
if (document.addEventListener) {
// first choice is DOMContentLoaded event
document.addEventListener("DOMContentLoaded", ready, false);
// backup is window load event
window.addEventListener("load", ready, false);
} else {
// must be IE
document.attachEvent("onreadystatechange", readyStateChange);
window.attachEvent("onload", ready);
}
readyEventHandlersInstalled = true;
}
}
})("docReady", window);
用法：
// pass a function reference
docReady(fn);
// use an anonymous function
docReady(function() {
// code here
});
// pass a function reference and a context
// the context will be passed to the function as the first argument
docReady(fn, context);
// use an anonymous function with a context
docReady(function(context) {
// code here that can use the context argument that was passed to docReady
}, ctx);
已在以下位置进行了测试：
IE6 and up
Firefox 3.6 and up
Chrome 14 and up
Safari 5.1 and up
Opera 11.6 and up
Multiple iOS devices
Multiple Android devices
以下是其工作原理的摘要：
docReady()向其注册的处理程序保证按其注册顺序触发。
如果您docReady(fn)在文档准备就绪后调用，则将计划使用当前执行线程完成后立即执行回调setTimeout(fn, 1)。这使调用代码始终可以认为它们是异步回调，即使稍后在当前JS线程完成并保留调用顺序时也将稍后调用。
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