我们发现了一个快速而肮脏的跨浏览器实现，它可以用最少的实现实现大多数简单情况：

window.onReady = function onReady(fn){
    document.body ? fn() : setTimeout(function(){ onReady(fn);},50);
};

有一种基于标准的替代品DOMContentLoaded，99%以上的浏览器都支持它，但IE8:

document.addEventListener("DOMContentLoaded", function(event) { 
  //do work
});

jQuery的本机函数比window.onload复杂得多，如下所示。

function bindReady(){
    if ( readyBound ) return;
    readyBound = true;

    // Mozilla, Opera and webkit nightlies currently support this event
    if ( document.addEventListener ) {
        // Use the handy event callback
        document.addEventListener( "DOMContentLoaded", function(){
            document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
            jQuery.ready();
        }, false );

    // If IE event model is used
    } else if ( document.attachEvent ) {
        // ensure firing before onload,
        // maybe late but safe also for iframes
        document.attachEvent("onreadystatechange", function(){
            if ( document.readyState === "complete" ) {
                document.detachEvent( "onreadystatechange", arguments.callee );
                jQuery.ready();
            }
        });

        // If IE and not an iframe
        // continually check to see if the document is ready
        if ( document.documentElement.doScroll && window == window.top ) (function(){
            if ( jQuery.isReady ) return;

            try {
                // If IE is used, use the trick by Diego Perini
                // http://javascript.nwbox.com/IEContentLoaded/
                document.documentElement.doScroll("left");
            } catch( error ) {
                setTimeout( arguments.callee, 0 );
                return;
            }

            // and execute any waiting functions
            jQuery.ready();
        })();
    }

    // A fallback to window.onload, that will always work
    jQuery.event.add( window, "load", jQuery.ready );
}

以下是测试DOM就绪的最小代码片段，它适用于所有浏览器（甚至IE 8）：

r(function(){
    alert('DOM Ready!');
});
function r(f){/in/.test(document.readyState)?setTimeout('r('+f+')',9):f()}

看到这个答案。

大多数普通的JS Ready函数都不考虑在文档加载后设置DOMContentLoaded处理程序的情况——这意味着函数永远不会运行。如果在异步外部脚本（<script async src=“file.js”></script>）中查找DOMContentLoaded，则可能会发生这种情况。

只有当文档的readyState尚未交互或完成时，下面的代码才会检查DOMContentLoaded。

var DOMReady = function(callback) {
  document.readyState === "interactive" || document.readyState === "complete" ? callback() : document.addEventListener("DOMContentLoaded", callback());
};
DOMReady(function() {
  //DOM ready!
});

如果您也想支持IE：

var DOMReady = function(callback) {
    if (document.readyState === "interactive" || document.readyState === "complete") {
        callback();
    } else if (document.addEventListener) {
        document.addEventListener('DOMContentLoaded', callback());
    } else if (document.attachEvent) {
        document.attachEvent('onreadystatechange', function() {
            if (document.readyState != 'loading') {
                callback();
            }
        });
    }
};

DOMReady(function() {
  // DOM ready!
});

穷人的解决方案：

var checkLoad = function() {   
    document.readyState !== "complete" ? setTimeout(checkLoad, 11) : alert("loaded!");   
};  

checkLoad();  

查看Fiddle

添加了这个，我想更好一点，自己的范围，非递归

(function(){
    var tId = setInterval(function() {
        if (document.readyState == "complete") onComplete()
    }, 11);
    function onComplete(){
        clearInterval(tId);    
        alert("loaded!");    
    };
})()

查看Fiddle

使用纯JavaScript的最简单方法。没有jQuery：

document.addEventListener("DOMContentLoaded", function(event) {
   // Your code to run since DOM is loaded and ready
});