IE系列直到IE9才支持DOMContentLoaded事件，对于IE8及其之前版本，如果html内没有框架，则可以采用document.documentELement.doScroll来判断

是否构建好DOM树；如果html内有框架，则利用document的onreadystatechange事件判断当前DOM树是否构建完毕（框架html内容（只是html文件）加载之后DOM树构建完毕）。

所以可以采用这种方式：

　　

/**         * 实现DomContentLoaded的兼容性         * @param callback         */        var onDomContentLoaded = function(callback){            var onlyOnce = true;            var onReady = function(callback){                if(onlyOnce){                    onlyOnce = false;                    onDomContentLoaded.isDomReady = true;                    try{                        callback();                    }catch(e){                        throw(new Error('DOM Ready callback occurs an error!'))                    }                }                return;            }            if(S.browser.isIe && !('HTMLElement' in window)){  // lt IE9                if(self.top === self){                    function s(){                        try{                            document.documentElement.doScroll('left');                            onReady(callback);                            return;                        }catch(e){                            setTimeout(s,50);                        }                    }                    s();                }else{ //包含框架                    document.attachEvent('onreadystatechange',function(){                        if(document.readyState === 'complete'){                            onReady(callback);                            document.detachEvent('onreadystatechange',arguments.callee);                        }                    });                }                document.onload = function(){                    onReady(callback);                    document.onload = null;                };            }else{                document.addEventListener('DOMContentLoaded',function(){                    onReady(callback);                    document.removeEventListener('DOMContentLoaded',arguments.callee);                },false);                document.onload = function(){                    onReady(callback);                    document.onload = null;                };            }        };

另外，John Resig也在《精通javascript》提出了一种方法来判断DOM是否构建完毕，那就是不断轮训判断

if(document && document.getElementById && document.getElementsByTagName && document.body)是否为true，若为true，则

DOM构建完毕。

最后，给出David Flanagan所给出的whenReady函数，很有技巧性：

　　

/* * Pass a function to whenReady() and it will be invoked (as a method of the * document) when the document is parsed and ready for manipulation. Registered * functions are triggered by the first DOMContentLoaded, readystatechange, or * load event that occurs. Once the document is ready and all functions have * been invoked, any functions passed to whenReady() will be invoked  * immediately. */var whenReady = (function() { // This function returns the whenReady() function    var funcs = [];    // The functions to run when we get an event    var ready = false; // Switches to true when the handler is triggered    // The event handler invoked when the document becomes ready    function handler(e) {        // If we've already run once, just return        if (ready) return;        // If this was a readystatechange event where the state changed to        // something other than "complete", then we're not ready yet        if (e.type === "readystatechange" && document.readyState !== "complete")            return;                // Run all registered functions.        // Note that we look up funcs.length each time, in case calling        // one of these functions causes more functions to be registered.        for(var i = 0; i < funcs.length; i++)             funcs[i].call(document);        // Now set the ready flag to true and forget the functions        ready = true;        funcs = null;    }    // Register the handler for any event we might receive    if (document.addEventListener) {        document.addEventListener("DOMContentLoaded", handler, false);        document.addEventListener("readystatechange", handler, false);        window.addEventListener("load", handler, false);    }    else if (document.attachEvent) {        document.attachEvent("onreadystatechange", handler);        window.attachEvent("onload", handler);    }    // Return the whenReady function    return function whenReady(f) {        if (ready) f.call(document); // If already ready, just run it        else funcs.push(f);          // Otherwise, queue it for later.    }}());