javascript:如何在没有 jquery 的情况下编写 $(document).ready 之类的事件

Question

在 jquery $(document).ready(function) 或 $(function) 中，没有 jquery 我怎么能做同样的事情，我需要浏览器兼容，并允许附加多个函数。

注意:dom ready!= window onload

Answer 1

这是 jQuery 包装您正在寻找的函数的方式 - 代码片段不需要 jQuery，并且跨浏览器兼容。我已将所有对 jQuery.ready() 的调用替换为 yourcallback - 您需要定义它。

这里发生了什么:

• 首先，定义函数 DOMContentLoaded，它将在 DOMContentLoaded 事件触发时使用 - 它确保回调仅被调用一次。
• 检查文档是否已经加载 - 如果是，立即触发回调
• 否则嗅探功能(document.addEventListener/document.attachEvent)并将回调绑定(bind)到它(IE 和普通浏览器不同，加上 onload 回调)

Lifted from jQuery 1.4.3, functions bindReady() and DOMContentLoaded :

/*
* Copyright 2010, John Resig
* Dual licensed under the MIT or GPL Version 2 licenses.
* http://jquery.org/license
*/
// Cleanup functions for the document ready method
// attached in the bindReady handler
if ( document.addEventListener ) {
DOMContentLoaded = function() {
    document.removeEventListener( "DOMContentLoaded", DOMContentLoaded, false );
    //jQuery.ready();
            yourcallback();
};

} else if ( document.attachEvent ) {
DOMContentLoaded = function() {
    // Make sure body exists, at least, in case IE gets a little overzealous 
            if ( document.readyState === "complete" ) {
        document.detachEvent( "onreadystatechange", DOMContentLoaded );
        //jQuery.ready();
                    yourcallback();
    }
    };
}

// 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 );
    // ^^ you may want to call *your* function here, similarly for the other calls to jQuery.ready
    setTimeout( yourcallback, 1 );
}

// Mozilla, Opera and webkit nightlies currently 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 );
    window.addEventListener( "load", yourcallback, 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", yourcallback );

 }

那是 51 行纯 JavaScript 代码，只是为了可靠地注册事件。据我所知，没有更简单的方法。将展示像 jQuery 这样的包装器有什么好处:它们包装了功能嗅探和丑陋的兼容性问题，以便您可以专注于其他事情。