页面初始化中,用的较多的就是$(document).ready(function(){//代码}); 或 $(window).load(function(){//代码});他们的区别就是,ready是在DOM的结构加载完后就触发,load是在页面内包括DOM结构,css,js,图 ...
页面初始化中,用的较多的就是$(document).ready(function(){//代码}); 或 $(window).load(function(){//代码});
他们的区别就是,ready是在DOM的结构加载完后就触发,load是在页面内包括DOM结构,css,js,图片等都加载完成后再触发,显然ready更适合作为页面初始化使用。但有时候也不尽然。需要进一步查看其内部机制。
那么ready的内部是如何判断DOM的结构加载完的?并且不同的浏览器的判断是如何的?
答案就在jquery代码内,假设jquery的版本是jquery-1.11.3.js。
ready的关键代码(3507~3566行),关键代码用红色标出:
jQuery.ready.promise = function( obj ) { if ( !readyList ) { readyList = jQuery.Deferred(); // Catch cases where $(document).ready() is called after the browser event has already occurred. // we once tried to use readyState "interactive" here, but it caused issues like the one // discovered by ChrisS here: http://bugs.jquery.com/ticket/12282#comment:15 if ( document.readyState === "complete" ) { // Handle it asynchronously to allow scripts the opportunity to delay ready setTimeout( jQuery.ready ); // Standards-based browsers support DOMContentLoaded } else if ( document.addEventListener ) { // Use the handy event callback document.addEventListener( "DOMContentLoaded", completed, false ); // A fallback to window.onload, that will always work window.addEventListener( "load", completed, false ); // If IE event model is used } else { // Ensure firing before onload, maybe late but safe also for iframes document.attachEvent( "onreadystatechange", completed ); // A fallback to window.onload, that will always work window.attachEvent( "onload", completed ); // If IE and not a frame // continually check to see if the document is ready var top = false; try { top = window.frameElement == null && document.documentElement; } catch(e) {} if ( top && top.doScroll ) { (function doScrollCheck() { if ( !jQuery.isReady ) { try { // Use the trick by Diego Perini // http://javascript.nwbox.com/IEContentLoaded/ top.doScroll("left"); } catch(e) { return setTimeout( doScrollCheck, 50 ); } // detach all dom ready events detach(); // and execute any waiting functions jQuery.ready(); } })(); } } } return readyList.promise( obj );};
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原标题:jquery的ready事件的实现机制浅析
关键词:jquery
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