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HomeWeb Front-endJS TutorialDom加载让图片加载完再执行的脚本代码_javascript技巧

现在,我们来研究一下如何解决这个问题,解决方法就是在DOM加载完毕之后就执行程序。 

       先介绍两个人。一,jquery的作者:John Resig;二,javascript的世界级大师:dean edwards。(大家要记住这两位天才!) 

      jquery里有专门解决DOM加载的函数$(document).ready()(简写就是$(fn)),非常好用!John Resig在《Pro JavaScript Techniques》里,有这样一个方法处理DOM加载,原理就是通过document&& document.getElementsByTagName &&document.getElementById&& document.body 去判断Dom树是否加载完毕。代码如下:

复制代码 代码如下:

function domReady( f ) {
// 如果DOM加载完毕,马上执行函数
if ( domReady.done ) return f();   
// 假如我们已增加一个函数
if ( domReady.timer ) { 
// 把它加入待执行的函数清单中
domReady.ready.push( f ); 
} else { 
// 为页面加载完成绑定一个事件, 
// 为防止它最先完成. 使用 addEvent(下面列出).
addEvent( window, “load”, isDOMReady );   
// 初始化待执行的函数的数组
domReady.ready = [ f ];   
// 经可能快地检查Dom是否已可用
domReady.timer = setInterval( isDOMReady, 13 ); 

}  
// 检查Dom是否已可操作
function isDOMReady() { 
// 假如已检查出Dom已可用, 忽略 
if ( domReady.done ) return false;   
// 检查若干函数和元素是否可用
if ( document &&  document.getElementsByTagName &&  document.getElementById &&  document.body ) {   
// 假如可用, 停止检查
clearInterval( domReady.timer ); 
domReady.timer = null;   
// 执行所有等待的函数
for ( var i = 0; i domReady.ready[i]();   
// 记录在此已经完成
domReady.ready = null; 
domReady.done = true; 

}
// 由 Dean Edwards 在2005 所编写addEvent/removeEvent,
// 由 Tino Zijdel整理
// http://dean.edwards.name/weblog/2005/10/add-event/
//优点是1.可以在所有浏览器工作;
//2.this指向当前元素;
//3.综合了所有浏览器防止默认行为和阻止事件冒泡的的函数
//缺点就是仅在冒泡阶段工作
function addEvent(element, type, handler) {
    // assign each event handler a unique ID
    if (!handler.$$guid) handler.$$guid = addEvent.guid++;
    // create a hash table of event types for the element
    if (!element.events) element.events = {};
    // create a hash table of event handlers for each element/event pair
    var handlers = element.events[type];
    if (!handlers) {
        handlers = element.events[type] = {};
        // store the existing event handler (if there is one)
        if (element["on" + type]) {
            handlers[0] = element["on" + type];
        }
    }
    // store the event handler in the hash table
    handlers[handler.$$guid] = handler;
    // assign a global event handler to do all the work
    element["on" + type] = handleEvent;
};
// a counter used to create unique IDs
addEvent.guid = 1;
function removeEvent(element, type, handler) {
    // delete the event handler from the hash table
    if (element.events && element.events[type]) {
        delete element.events[type][handler.$$guid];
    }
};
function handleEvent(event) {
    var returnValue = true;
    // grab the event object (IE uses a global event object)
    event = event || fixEvent(window.event);
    // get a reference to the hash table of event handlers
    var handlers = this.events[event.type];
    // execute each event handler
    for (var i in handlers) {
        this.$$handleEvent = handlers[i];
        if (this.$$handleEvent(event) === false) {
            returnValue = false;
        }
    }
    return returnValue;
};
function fixEvent(event) {
    // add W3C standard event methods
    event.preventDefault = fixEvent.preventDefault;
    event.stopPropagation = fixEvent.stopPropagation;
    return event;
};
fixEvent.preventDefault = function() {
    this.returnValue = false;
};
fixEvent.stopPropagation = function() {
    this.cancelBubble = true;
};

还有一个估计由几个外国大师合作写的,实现同样功能。
复制代码 代码如下:

/*
* (c)2006 Jesse Skinner/Dean Edwards/Matthias Miller/John Resig
* Special thanks to Dan Webb's domready.js Prototype extension
* and Simon Willison's addLoadEvent
*
* For more info, see:
* http://www.thefutureoftheweb.com/blog/adddomloadevent
* http://dean.edwards.name/weblog/2006/06/again/
* http://www.vivabit.com/bollocks/2006/06/21/a-dom-ready-extension-for-prototype
* http://simon.incutio.com/archive/2004/05/26/addLoadEvent

*
* To use: call addDOMLoadEvent one or more times with functions, ie:
*
*    function something() {
*       // do something
*    }
*    addDOMLoadEvent(something);
*
*    addDOMLoadEvent(function() {
*        // do other stuff
*    });
*
*/

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())
                exec();
            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><\/scr"+"ipt>"); <BR> script = document.getElementById("__ie_onload"); <BR> script.onreadystatechange = function() { <BR> if (this.readyState == "complete") <BR> init(); // call the onload handler <BR> }; <BR> /*@end @*/ <BR> // for Safari <BR> if (/WebKit/i.test(navigator.userAgent)) { // sniff <BR> load_timer = setInterval(function() { <BR> if (/loaded|complete/.test(document.readyState)) <BR> init(); // call the onload handler <BR> }, 10); <BR> } <BR> // for other browsers set the window.onload, but also execute the old window.onload <BR> old_onload = window.onload; <BR> window.onload = function() { <BR> init(); <BR> if (old_onload) old_onload(); <BR> }; <BR> } <BR> load_events.push(func); <BR> } <BR>})();<BR></script>
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