DOMContentLoaded事件

今天查看百度空间源代码，发现多了个util.js文件，打开看看。里面里面定义了addDOMLoadEvent。这是干什么用的？

仔细查看代码，发现在Mozilla添加了DOMContentLoaded事件，这个在以前一直没有用过。                    if (document.addEventListener)
                        document.addEventListener("DOMContentLoaded", init, false);

好久就是为了兼容实现DOMContentLoaded事件。

网上找了点有关DOMContentLoaded的资料拿来看看。

DOMContentLoaded是firefox下特有的Event, 当所有DOM解析完以后会触发这个事件。
    与DOM中的onLoad事件与其相近。但onload要等到所有页面元素加载完成才会触发, 包括页面上的图片等等。
    如果页面的图片很多的话, 从用户访问到onload触发可能需要较长的时间, 而在Ajax运用中, 常常需要在onload中加入许多初始化的动作, 如果由于网络问题引起的图片加载过慢( 见: Ajax优化(2) -- lazierLoad img && js), 则必然影响用户的体验。
    在这种情况下firefox的DOMContentLoaded事件, 恰恰是我们需要的。

    目前,跨平台的DOMContentLoaded的解决方案有很多, 比如jQuery, Prototype...等等, 其实现原理大同小异.

    在项目中, 我使用了Prototype工具, 以往调用初始化的方法是:

Event.observe(window, "load", init);

    现在有了DOMContentLoaded, 可以替换成如下的方法:

document.observe('contentloaded', init);

    最新的prototype中自定义事件已经重新命名, 使用"dom:loaded" 代替了 “contentloaded”.

document.observe('dom:loaded', init);

附:

   Andrea Giammarchi的OnContent函数提供了一个跨平台的DOMContentLoaded的解决方案My DOMContentLoaded Final Solution 

文件名称：DOMContentLoaded.js

1. function onContent(f){
2.     var a = onContent,
3.      b = navigator.userAgent,
4.      d = document,
5.      w = window,
6.      c = "onContent",
7.     e = "addEventListener",
8.      o = "opera",
9.      r = "readyState",
10.      s = "<scr".concat("ipt defer src='//:' on", r, "change='if(this.", r, "==\"complete\"){this.parentNode.removeChild(this);", c, ".", c, "()}'></scr", "ipt>");
11.      a[c] = (function(o) {
12.         return function() {
13.              a[c] = function() {};
14.             for (a = arguments.callee; ! a.done; a.done = 1) f(o ? o() : o)
15.         }
16.     })(a[c]);
17.     if (d[e]) d[e]("DOMContentLoaded", a[c], false);
18.     if (/WebKit|Khtml/i.test(b) || (w[o] && parseInt(w[o].version()) < 9))(function() { / loaded | complete / .test(d[r]) ? a[c]() : setTimeout(arguments.callee, 1)
19.     })();
20.     else if (/MSIE/i.test(b)) d.write(s);
22. };

util.js：

addDOMLoadEvent = (function(){
        // create event function stack
        var load_events = [],
            load_timer,
            script,
            done,
            exec,
            old_onload,
            init = function () {
                done = true;
                // kill the timer
                clearInterval(load_timer);

                // execute each function in the stack in the order they were added
                while (exec = load_events.shift())
                    setTimeout(exec, 10);
                if (script) script.onreadystatechange = '';
            };

            return function (func) {
                // if the init function was already ran, just run this function now and stop
                if (done) return func();

                if (!load_events[0]) {
                    // for Mozilla/Opera9
                    if (document.addEventListener)
                        document.addEventListener("DOMContentLoaded", init, false);

                    // for Internet Explorer

                    /*@cc_on @*/
                    /*@if (@_win32)
                        document.write("<script id=__ie_onload defer src=//0><\/scr"+"ipt>");
                        script = document.getElementById("__ie_onload");
                        script.onreadystatechange = function() {
                            if (this.readyState == "complete")
                                init(); // call the onload handler
                        };
                    /*@end @*/

                    // for Safari
                    if (/WebKit/i.test(navigator.userAgent)) { // sniff
                        load_timer = setInterval(function() {
                            if (/loaded|complete/.test(document.readyState))
                                init(); // call the onload handler
                        }, 10);
                    }

                    // for other browsers set the window.onload, but also execute the old window.onload
                    old_onload = window.onload;

                    window.onload = function() {
                        init();
                        if (old_onload) old_onload();
                    };
                }

            load_events.push(func);
        }
})();

function insertWBR(string, step){
    var textarea = document.createElement('TEXTAREA');
    textarea.innerHTML = string.replace(/</g,"&lt;").replace(/>/g,"&gt;");
    string = textarea.value;

    var step = (step || 5), reg = new RegExp("({" + step + "})", "gi");
    return string.replace(/(<[^>]+>)/gi,"$1<wbr/>").replace(/(>|^)([^<]+)(<|$)/gi, function(a,b,c,d){
        if(c.length < step) return a;
        return b + c.replace(reg, "$1<wbr/>") + d;
    });
}