我有一个使用$(document).ready的脚本,但它不使用jQuery中的任何其他内容。我想通过删除jQuery依赖项来减轻它。
如何在不使用jQuery的情况下实现我自己的$(document).ready功能?我知道,使用window.onload将不同,因为window.onlead在加载所有图像、帧等后启动。
我有一个使用$(document).ready的脚本,但它不使用jQuery中的任何其他内容。我想通过删除jQuery依赖项来减轻它。
如何在不使用jQuery的情况下实现我自己的$(document).ready功能?我知道,使用window.onload将不同,因为window.onlead在加载所有图像、帧等后启动。
当前回答
现在是2020年,<script>标签具有defer属性。
例如:
<script src="demo_defer.js" defer></script>
它指定当页面完成解析时执行脚本。
https://www.w3schools.com/tags/att_script_defer.asp
其他回答
一旦DOM就绪,此跨浏览器代码将调用函数:
var domReady=function(func){
var scriptText='('+func+')();';
var scriptElement=document.createElement('script');
scriptElement.innerText=scriptText;
document.body.appendChild(scriptElement);
};
以下是它的工作原理:
domReady的第一行调用函数的toString方法,以获取传入函数的字符串表示形式,并将其包装在立即调用该函数的表达式中。domReady的其余部分使用表达式创建一个脚本元素,并将其附加到文档正文中。DOM就绪后,浏览器运行附加到主体的脚本标记。
例如,如果您这样做:domReady(function(){alert();});,以下内容将附加到body元素:
<script>(function (){alert();})();</script>
注意,这只适用于用户定义的函数。以下命令不起作用:domReady(警报);
我最近在一个移动网站上使用这个。这是John Resig的简化版“Pro JavaScript技术”。它取决于addEvent。
var ready = ( function () {
function ready( f ) {
if( ready.done ) return f();
if( ready.timer ) {
ready.ready.push(f);
} else {
addEvent( window, "load", isDOMReady );
ready.ready = [ f ];
ready.timer = setInterval(isDOMReady, 13);
}
};
function isDOMReady() {
if( ready.done ) return false;
if( document && document.getElementsByTagName && document.getElementById && document.body ) {
clearInterval( ready.timer );
ready.timer = null;
for( var i = 0; i < ready.ready.length; i++ ) {
ready.ready[i]();
}
ready.ready = null;
ready.done = true;
}
}
return ready;
})();
适用于所有已知的浏览器(通过BrowserStack测试)。IE6+、Safari 1+、Chrome 1+、Opera等。使用DOMContentLoaded,带有document.dococumentElement.doScroll()和window.onload的回退。
/*! https://github.com/Kithraya/DOMContentLoaded v1.2.6 | MIT License */
DOMContentLoaded.version = "1.2.6";
function DOMContentLoaded() { "use strict";
var ael = 'addEventListener', rel = 'removeEventListener', aev = 'attachEvent', dev = 'detachEvent';
var alreadyRun = false, // for use in the idempotent function ready()
funcs = arguments;
// old versions of JS return '[object Object]' for null.
function type(obj) { return (obj === null) ? 'null' : Object.prototype.toString.call(obj).slice(8,-1).toLowerCase() }
function microtime() { return + new Date() }
/* document.readyState === 'complete' reports correctly in every browser I have tested, including IE.
But IE6 to 10 don't return the correct readyState values as per the spec:
readyState is sometimes 'interactive', even when the DOM isn't accessible in IE6/7 so checking for the onreadystatechange event like jQuery does is not optimal
readyState is complete at basically the same time as 'window.onload' (they're functionally equivalent, within a few tenths of a second)
Accessing undefined properties of a defined object (document) will not throw an error (in case readyState is undefined).
*/
// Check for IE < 11 via conditional compilation
/// values: 5?: IE5, 5.5?: IE5.5, 5.6/5.7: IE6/7, 5.8: IE8, 9: IE9, 10: IE10, 11*: (IE11 older doc mode), undefined: IE11 / NOT IE
var jscript_version = Number( new Function("/*@cc_on return @_jscript_version; @*\/")() ) || NaN;
// check if the DOM has already loaded
if (document.readyState === 'complete') { ready(null); return; } // here we send null as the readyTime, since we don't know when the DOM became ready.
if (jscript_version < 9) { doIEScrollCheck(); return; } // For IE<9 poll document.documentElement.doScroll(), no further actions are needed.
/*
Chrome, Edge, Firefox, IE9+, Opera 9+, Safari 3.1+, Android Webview, Chrome for Android, Edge Mobile,
Firefox for Android 4+, Opera for Android, iOS Safari, Samsung Internet, etc, support addEventListener
And IE9+ supports 'DOMContentLoaded'
*/
if (document[ael]) {
document[ael]("DOMContentLoaded", ready, false);
window[ael]("load", ready, false); // fallback to the load event in case addEventListener is supported, but not DOMContentLoaded
} else
if (aev in window) { window[aev]('onload', ready);
/* Old Opera has a default of window.attachEvent being falsy, so we use the in operator instead
https://dev.opera.com/blog/window-event-attachevent-detachevent-script-onreadystatechange/
Honestly if somebody is using a browser so outdated AND obscure (like Opera 7 where neither addEventListener
nor "DOMContLoaded" is supported, they deserve to wait for the full page).
I CBA testing whether readyState === 'interactive' is truly interactive in browsers designed in 2003. I just assume it isn't (like in IE6-8).
*/
} else { // fallback to queue window.onload that will always work
addOnload(ready);
}
// This function allows us to preserve any original window.onload handlers (in super old browsers where this is even necessary),
// while keeping the option to chain onloads, and dequeue them.
function addOnload(fn) { var prev = window.onload; // old window.onload, which could be set by this function, or elsewhere
// we add a function queue list to allow for dequeueing
// addOnload.queue is the queue of functions that we will run when when the DOM is ready
if ( type( addOnload.queue ) !== 'array') { addOnload.queue = [];
if ( type(prev) === 'function') { addOnload.queue.push( prev ); } // add the previously defined event handler
}
if (typeof fn === 'function') { addOnload.queue.push(fn) }
window.onload = function() { // iterate through the queued functions
for (var i = 0; i < addOnload.queue.length; i++) { addOnload.queue[i]() }
};
}
// remove a queued window.onload function from the chain (simplified);
function dequeueOnload(fn) { var q = addOnload.queue, i = 0;
// sort through the queued functions in addOnload.queue until we find `fn`
if (type( q ) === 'array') { // if found, remove from the queue
for (; i < q.length; i++) { ;;(fn === q[i]) ? q.splice(i, 1) : 0; } // void( (fn === q[i]) ? q.splice(i, 1) : 0 )
}
}
function ready(ev) { // idempotent event handler function
if (alreadyRun) {return} alreadyRun = true;
// this time is when the DOM has loaded (or if all else fails, when it was actually possible to inference the DOM has loaded via a 'load' event)
// perhaps this should be `null` if we have to inference readyTime via a 'load' event, but this functionality is better.
var readyTime = microtime();
detach(); // detach any event handlers
// run the functions
for (var i=0; i < funcs.length; i++) { var func = funcs[i];
if (type(func) === 'function') {
func.call(document, { 'readyTime': (ev === null ? null : readyTime), 'funcExecuteTime': microtime() }, func);
// jquery calls 'ready' with `this` being set to document, so we'll do the same.
}
}
}
function detach() {
if (document[rel]) {
document[rel]("DOMContentLoaded", ready); window[rel]("load", ready);
} else
if (dev in window) { window[dev]("onload", ready); }
else {
dequeueOnload(ready);
}
}
function doIEScrollCheck() { // for use in IE < 9 only.
if ( window.frameElement ) {
// we're in an <iframe> or similar
// the document.documentElemeent.doScroll technique does not work if we're not at the top-level (parent document)
try { window.attachEvent("onload", ready); } catch (e) { } // attach to onload if were in an <iframe> in IE as there's no way to tell otherwise
return;
}
try {
document.documentElement.doScroll('left'); // when this statement no longer throws, the DOM is accessible in old IE
} catch(error) {
setTimeout(function() {
(document.readyState === 'complete') ? ready() : doIEScrollCheck();
}, 50);
return;
}
ready();
}
}
用法:
<script>
DOMContentLoaded(function(e) { console.log(e) });
</script>
将<script>/*JavaScript代码*/</script>放在结束</body>标记之前。
诚然,这可能不符合每个人的目的,因为它需要更改HTML文件,而不仅仅是在JavaScript文件中做一些事情,比如document.ready,但是。。。
如果您正在加载BODY底部附近的jQuery,但在编写jQuery(<func>)或jQuery(document).ready(<func>)时遇到问题,请在Github上查看jqShim。
与其重新创建自己的文档就绪函数,它只需保留这些函数,直到jQuery可用,然后按预期继续jQuery。将jQuery移动到主体底部的目的是加快页面加载速度,您仍然可以通过在模板头部内联jqShim.min.js来实现这一点。
最后我写了这段代码,将WordPress中的所有脚本都移到了页脚,而现在只有这段填充码直接位于页眉中。