# 惰性初始模式 延遲初始化 是一種允許我們延遲初始化消耗資源比較大的進程，直到需要他們的時候（才初始化）。這其中的一個例子就是jQuery的.ready()方法，它在DOM節點加載完畢之后會執行一個回調方法。 ~~~ $( document ).ready( function () { //ajax請求不會執行，直到DOM加載完成 var jqxhr = $.ajax({ url: "http://domain.com/api/", data: "display=latest&order=ascending" }) .done( function( data ) ){ $(".status").html( "content loaded" ); console.log( "Data output:" + data ); }); }); ~~~ jQuery.fn.ready()底層是通過byjQuery.bindReady()來實現的, 如下所示: ~~~ bindReady: function() { if ( readyList ) { return; } readyList = jQuery.Callbacks( "once memory" ); // Catch cases where $(document).ready() is called after the // browser event has already occurred. if ( document.readyState === "complete" ) { // Handle it asynchronously to allow scripts the opportunity to delay ready return setTimeout( jQuery.ready, 1 ); } // Mozilla, Opera and webkit support this event if ( document.addEventListener ) { // Use the handy event callback document.addEventListener( "DOMContentLoaded", DOMContentLoaded, false ); // A fallback to window.onload, that will always work window.addEventListener( "load", jQuery.ready, false ); // If IE event model is used } else if ( document.attachEvent ) { // ensure firing before onload, // maybe late but safe also for iframes document.attachEvent( "onreadystatechange", DOMContentLoaded ); // A fallback to window.onload, that will always work window.attachEvent( "onload", jQuery.ready ); // If IE and not a frame // continually check to see if the document is ready var toplevel = false; try { toplevel = window.frameElement == null; } catch(e) {} if ( document.documentElement.doScroll && toplevel ) { doScrollCheck(); } } }, ~~~ 即使不直接在jQuery核心文件中使用，有些開發者通過一些插件也可能熟悉懶加載的概念，延遲加載和攬初始化一樣有效，它是一種在需要的時候（比如：當用戶瀏覽到了頁面底部的時候）才加載頁面數據的技術。最近幾年，這種模式已經變得非常顯著并且現在可以再Twitter和Facebook的UI里面zhaoda。