Posted in Javascript onMay 15, 2008
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:
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.length; 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。
/* * (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 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); } })();
Dom加载让图片加载完再执行的脚本代码
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