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
这很好https://stackoverflow.com/a/11810957/185565穷人的解决方案。一条评论认为，这是在紧急情况下纾困的一种对策。这是我的修改。
function doTheMagic(counter) {
alert("It worked on " + counter);
}
// wait for document ready then call handler function
var checkLoad = function(counter) {
counter++;
if (document.readyState != "complete" && counter<1000) {
var fn = function() { checkLoad(counter); };
setTimeout(fn,10);
} else doTheMagic(counter);
};
checkLoad(0);
其他回答
与jQuery相比，使用JavaScript等价物总是很好的。一个原因是依赖的库少了一个，而且它们比jQuery等同物快得多。
jQuery等价物的一个极好的参考是http://youmightnotneedjquery.com/.
就您的问题而言，我从上面的链接中获取了以下代码：）唯一需要注意的是，它仅适用于Internet Explorer 9及更高版本。
function ready(fn) {
if (document.readyState != 'loading') {
fn();
}
else {
document.addEventListener('DOMContentLoaded', fn);
}
}
编辑：
2023更新，请使用此项：
function ready(fn) {
if (document.readyState !== 'loading') {
fn();
return;
}
document.addEventListener('DOMContentLoaded', fn);
}
发件人：https://youmightnotneedjquery.com/
这里是jQuery的可行替代品
function ready(callback){
// in case the document is already rendered
if (document.readyState!='loading') callback();
// modern browsers
else if (document.addEventListener) document.addEventListener('DOMContentLoaded', callback);
// IE <= 8
else document.attachEvent('onreadystatechange', function(){
if (document.readyState=='complete') callback();
});
}
ready(function(){
// do something
});
摘自https://plainjs.com/javascript/events/running-code-when-the-document-is-ready-15/
另一个很好的domReady函数来自https://stackoverflow.com/a/9899701/175071
由于被接受的答案还远远没有完成，我根据jQuery1.6.2的源代码拼接了一个“ready”函数，如jQuery.ready（）：
var ready = (function(){
var readyList,
DOMContentLoaded,
class2type = {};
class2type["[object Boolean]"] = "boolean";
class2type["[object Number]"] = "number";
class2type["[object String]"] = "string";
class2type["[object Function]"] = "function";
class2type["[object Array]"] = "array";
class2type["[object Date]"] = "date";
class2type["[object RegExp]"] = "regexp";
class2type["[object Object]"] = "object";
var ReadyObj = {
// Is the DOM ready to be used? Set to true once it occurs.
isReady: false,
// A counter to track how many items to wait for before
// the ready event fires. See #6781
readyWait: 1,
// Hold (or release) the ready event
holdReady: function( hold ) {
if ( hold ) {
ReadyObj.readyWait++;
} else {
ReadyObj.ready( true );
}
},
// Handle when the DOM is ready
ready: function( wait ) {
// Either a released hold or an DOMready/load event and not yet ready
if ( (wait === true && !--ReadyObj.readyWait) || (wait !== true && !ReadyObj.isReady) ) {
// Make sure body exists, at least, in case IE gets a little overzealous (ticket #5443).
if ( !document.body ) {
return setTimeout( ReadyObj.ready, 1 );
}
// Remember that the DOM is ready
ReadyObj.isReady = true;
// If a normal DOM Ready event fired, decrement, and wait if need be
if ( wait !== true && --ReadyObj.readyWait > 0 ) {
return;
}
// If there are functions bound, to execute
readyList.resolveWith( document, [ ReadyObj ] );
// Trigger any bound ready events
//if ( ReadyObj.fn.trigger ) {
// ReadyObj( document ).trigger( "ready" ).unbind( "ready" );
//}
}
},
bindReady: function() {
if ( readyList ) {
return;
}
readyList = ReadyObj._Deferred();
// 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( ReadyObj.ready, 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", ReadyObj.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", ReadyObj.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();
}
}
},
_Deferred: function() {
var // callbacks list
callbacks = [],
// stored [ context , args ]
fired,
// to avoid firing when already doing so
firing,
// flag to know if the deferred has been cancelled
cancelled,
// the deferred itself
deferred = {
// done( f1, f2, ...)
done: function() {
if ( !cancelled ) {
var args = arguments,
i,
length,
elem,
type,
_fired;
if ( fired ) {
_fired = fired;
fired = 0;
}
for ( i = 0, length = args.length; i < length; i++ ) {
elem = args[ i ];
type = ReadyObj.type( elem );
if ( type === "array" ) {
deferred.done.apply( deferred, elem );
} else if ( type === "function" ) {
callbacks.push( elem );
}
}
if ( _fired ) {
deferred.resolveWith( _fired[ 0 ], _fired[ 1 ] );
}
}
return this;
},
// resolve with given context and args
resolveWith: function( context, args ) {
if ( !cancelled && !fired && !firing ) {
// make sure args are available (#8421)
args = args || [];
firing = 1;
try {
while( callbacks[ 0 ] ) {
callbacks.shift().apply( context, args );//shifts a callback, and applies it to document
}
}
finally {
fired = [ context, args ];
firing = 0;
}
}
return this;
},
// resolve with this as context and given arguments
resolve: function() {
deferred.resolveWith( this, arguments );
return this;
},
// Has this deferred been resolved?
isResolved: function() {
return !!( firing || fired );
},
// Cancel
cancel: function() {
cancelled = 1;
callbacks = [];
return this;
}
};
return deferred;
},
type: function( obj ) {
return obj == null ?
String( obj ) :
class2type[ Object.prototype.toString.call(obj) ] || "object";
}
}
// The DOM ready check for Internet Explorer
function doScrollCheck() {
if ( ReadyObj.isReady ) {
return;
}
try {
// If IE is used, use the trick by Diego Perini
// http://javascript.nwbox.com/IEContentLoaded/
document.documentElement.doScroll("left");
} catch(e) {
setTimeout( doScrollCheck, 1 );
return;
}
// and execute any waiting functions
ReadyObj.ready();
}
// Cleanup functions for the document ready method
if ( document.addEventListener ) {
DOMContentLoaded = function() {
document.removeEventListener( "DOMContentLoaded", DOMContentLoaded, false );
ReadyObj.ready();
};
} else if ( document.attachEvent ) {
DOMContentLoaded = function() {
// Make sure body exists, at least, in case IE gets a little overzealous (ticket #5443).
if ( document.readyState === "complete" ) {
document.detachEvent( "onreadystatechange", DOMContentLoaded );
ReadyObj.ready();
}
};
}
function ready( fn ) {
// Attach the listeners
ReadyObj.bindReady();
var type = ReadyObj.type( fn );
// Add the callback
readyList.done( fn );//readyList is result of _Deferred()
}
return ready;
})();
如何使用：
<script>
ready(function(){
alert('It works!');
});
ready(function(){
alert('Also works!');
});
</script>
我不确定这段代码的功能如何，但它在我的表面测试中运行良好。这花了很长时间，所以我希望你和其他人能从中受益。
PS.：我建议编译它。
或者你可以使用http://dustindiaz.com/smallest-domready-ever:
function r(f){/in/.test(document.readyState)?setTimeout(r,9,f):f()}
r(function(){/*code to run*/});
如果您只需要支持新的浏览器，则使用本机函数（与jQuery就绪不同，如果您在页面加载后添加此函数，则不会运行此函数）
document.addEventListener('DOMContentLoaded',function(){/*fun code to run*/})
最小且100%工作
我已经从PlainJS中选择了答案，它对我来说很好。它扩展了DOMContentLoaded，因此它可以在所有浏览器中被接受。
此函数等效于jQuery的$（document）.ready（）方法：
document.addEventListener('DOMContentLoaded', function(){
// do something
});
然而，与jQuery不同的是，这段代码只能在现代浏览器中正常运行（IE>8），如果在插入此脚本时（例如通过Ajax）已经呈现了文档，则无法正常运行。因此，我们需要稍微扩展一下：
function run() {
// do something
}
// in case the document is already rendered
if (document.readyState!='loading') run();
// modern browsers
else if (document.addEventListener)
document.addEventListener('DOMContentLoaded', run);
// IE <= 8
else document.attachEvent('onreadystatechange', function(){
if (document.readyState=='complete') run();
});
这基本上涵盖了所有的可能性，是jQuery助手的可行替代品。
有一种基于标准的替代品DOMContentLoaded，99%以上的浏览器都支持它，但IE8:
document.addEventListener("DOMContentLoaded", function(event) {
//do work
});
jQuery的本机函数比window.onload复杂得多，如下所示。
function bindReady(){
if ( readyBound ) return;
readyBound = true;
// Mozilla, Opera and webkit nightlies currently support this event
if ( document.addEventListener ) {
// Use the handy event callback
document.addEventListener( "DOMContentLoaded", function(){
document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
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", function(){
if ( document.readyState === "complete" ) {
document.detachEvent( "onreadystatechange", arguments.callee );
jQuery.ready();
}
});
// If IE and not an iframe
// continually check to see if the document is ready
if ( document.documentElement.doScroll && window == window.top ) (function(){
if ( jQuery.isReady ) return;
try {
// If IE is used, use the trick by Diego Perini
// http://javascript.nwbox.com/IEContentLoaded/
document.documentElement.doScroll("left");
} catch( error ) {
setTimeout( arguments.callee, 0 );
return;
}
// and execute any waiting functions
jQuery.ready();
})();
}
// A fallback to window.onload, that will always work
jQuery.event.add( window, "load", jQuery.ready );
}
使用纯JavaScript的最简单方法。没有jQuery：
document.addEventListener("DOMContentLoaded", function(event) {
// Your code to run since DOM is loaded and ready
});
