编辑：
这是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
});
取自
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
由于所接受的答案还远远不够完整，因此我将诸如jQuery.ready()基于jQuery 1.6.2源的“就绪”功能缝合在一起：
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>
我不确定此代码的功能如何，但在我的表面测试中效果很好。这花费了一段时间，所以我希望您和其他人可以从中受益。
PS .：我建议编译它。
或者，您可以使用http://dustindiaz.com/smallest-domready-ever：
function r(f){/in/.test(document.readyState)?setTimeout(r,9,f):f()}
r(function(){/*code to run*/});
或本机函数（如果您仅需要支持新的浏览器）（与jQuery ready不同，如果在页面加载后添加此功能，则该功能将无法运行）
document.addEventListener('DOMContentLoaded',function(){/*fun code to run*/})