I am writing an internal framework that can have no dependencies (i.e. jQuery, etc.) and am trying to implement my own DOM ready-style functionality. It seems that when a callback in the ready queue (array of callbacks to complete on DOM ready), if an exception is thrown inside that function, execution stops and continues onto the next callback (which is what I want), but Firefox will not report the error (log to the console, trigger onerror, anything). Am I doing something wrong?
I have implemented this using a combination of a pattern by Dean Edwards (http://dean.edwards.name/weblog/2009/03/callbacks-vs-events/) and the jQuery source. I do not wish to implement just like jQuery because if one callback fails, the subsequent callbacks won't execute.
var readyCallbacks = [];
(function () {
var currentHandler,
fireReady,
removeEvents,
loopCallbacks = function () {
for (var i = 0, len = readyCallbacks.length; i < len; i += 1) {
currentHandler = readyCallbacks[i];
fireReady();
}
};
if (document.addEventListener) {
document.addEventListener('readyEvents', function () { currentHandler(); }, false);
fireReady = function () {
var readyEvent = document.createEvent('UIEvents');
readyEvent.initEvent('readyEvents', false, false);
document.dispatchEvent(readyEvent);
};
removeEvents = function () {
window.removeEventListener('load', loopCallbacks, false);
loopCallbacks();
};
document.addEventListener('DOMContentLoaded', removeEvents, false);
window.addEventListener('load', loopCallbacks, false);
} else {
// if < IE 9
document.documentElement.readyEvents = 0;
document.documentElement.attachEvent('onpropertychange', function (e) {
if (e.propertyName === 'readyEvents')
currentHandler();
});
fireReady = function () {
document.documentElement.readyEvents += 1;
};
removeEvents = function () {
window.detachEvent('onload', loopCallbacks);
loopCallbacks();
};
document.attachEvent('onreadystatechange', removeEvents);
window.attachEvent('onload', loopCallbacks);
}
})();
Client.ready = function (callback) {
readyCallbacks.push(callback);
};
Here is my test implementation. The console is written to and the DOM element has been manipulated. In IE error with the UNDEFINED_VARIABLE++; is shown in the console, but not in Firefox.
<!DOCTYPE html>
<html>
<head>
<script src="Client.js"></script>
<script>
Client.ready(function () {
console.log('logging before error');
UNDEFINED_VARIABLE++; // This does not error in Firefox
console.log('logging after error, not logged in Firefox');
});
Client.ready(function () {
console.log('before DOM access');
document.getElementById('cheese').innerHTML = 'cheese';
console.log('after DOM access');
});
</script>
</head>
<body>
<div id="cheese">test</div>
</body>
</html>
After some searching, this appears to be a known Mozilla bug: Errors thrown by handlers for custom events dispatched via dispatchEvent() are not logged properly in some versions of Firefox 3.x. This isn't a problem in your code, but in the browser implementation. If it's a real problem for you, you can wrap the handler in a try/catch block to identify and deal with errors:
document.addEventListener('readyEvents', function() {
try { currentHandler() } catch (e) { console.log(e) }
}, false);
I have a jsFiddle here that demonstrates the problem with a simplified set of tests. Firefox correctly logs errors on handlers for built-in events like DOMContentLoaded and load, but misses the error when firing a handler for a custom event.
It's hard to get it right. See the jQuery source code and search for ready to see how it is implemented in a portable way. Keep in mind that you have to make sure that when you bind ready handlers after the dom is already ready then you have to call them straight away or else they won't be called at all. See also this question.
I have a script that uses $(document).ready, but it doesn't use anything else from jQuery. I'd like to lighten it up by removing the jQuery dependency.
How can I implement my own $(document).ready functionality without using jQuery? I know that using window.onload will not be the same, as window.onload fires after all images, frames, etc. have been loaded.
There is a standards based replacement,DOMContentLoaded that is supported by over 99% of browsers, though not IE8:
document.addEventListener("DOMContentLoaded", function(event) {
//do work
});
jQuery's native function is much more complicated than just window.onload, as depicted below.
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 );
}
Edit:
2023 update, use this:
function ready(fn) {
if (document.readyState !== 'loading') {
fn();
return;
}
document.addEventListener('DOMContentLoaded', fn);
}
From: https://youmightnotneedjquery.com/
Here is a viable replacement for jQuery ready
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
});
Taken from
https://plainjs.com/javascript/events/running-code-when-the-document-is-ready-15/
Another good domReady function here taken from https://stackoverflow.com/a/9899701/175071
As the accepted answer was very far from complete, I stitched together a "ready" function like jQuery.ready() based on jQuery 1.6.2 source:
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;
})();
How to use:
<script>
ready(function(){
alert('It works!');
});
ready(function(){
alert('Also works!');
});
</script>
I am not sure how functional this code is, but it worked fine with my superficial tests. This took quite a while, so I hope you and others can benefit from it.
PS.: I suggest compiling it.
Or you can use http://dustindiaz.com/smallest-domready-ever:
function r(f){/in/.test(document.readyState)?setTimeout(r,9,f):f()}
r(function(){/*code to run*/});
or the native function if you only need to support the new browsers (Unlike jQuery ready, this won't run if you add this after the page has loaded)
document.addEventListener('DOMContentLoaded',function(){/*fun code to run*/})
Three options:
If script is the last tag of the body, the DOM would be ready before script tag executes
When the DOM is ready, "readyState" will change to "complete"
Put everything under 'DOMContentLoaded' event listener
onreadystatechange
document.onreadystatechange = function () {
if (document.readyState == "complete") {
// document is ready. Do your stuff here
}
}
Source: MDN
DOMContentLoaded
document.addEventListener('DOMContentLoaded', function() {
console.log('document is ready. I can sleep now');
});
Concerned about stone age browsers:
Go to the jQuery source code and use the ready function. In that case you are not parsing+executing the whole library you're are doing only a very small part of it.
Place your <script>/*JavaScript code*/</script> right before the closing </body> tag.
Admittedly, this might not suit everyone's purposes since it requires changing the HTML file rather than just doing something in the JavaScript file a la document.ready, but still...
Poor man's solution:
var checkLoad = function() {
document.readyState !== "complete" ? setTimeout(checkLoad, 11) : alert("loaded!");
};
checkLoad();
View Fiddle
Added this one, a bit better I guess, own scope, and non recursive
(function(){
var tId = setInterval(function() {
if (document.readyState == "complete") onComplete()
}, 11);
function onComplete(){
clearInterval(tId);
alert("loaded!");
};
})()
View Fiddle
I use this:
document.addEventListener("DOMContentLoaded", function(event) {
//Do work
});
Note: This probably only works with newer browsers, especially these: http://caniuse.com/#feat=domcontentloaded
It is year 2020 and <script> tag has defer attribute.
for example:
<script src="demo_defer.js" defer></script>
it specifies that the script is executed when the page has finished parsing.
https://www.w3schools.com/tags/att_script_defer.asp
2022 version
In 2022, all you need to do is put the defer attribute on your script, and load it in the head!
Reference: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-defer
<!doctype html>
<html>
<head>
<script src="/script.js" defer></script>
</head>
<body>
<p>In 2022, all you need to do is put the defer attribute on your script, and load it in the head!</p>
</body>
</html>
This question was asked quite a long time ago. For anyone just seeing this question, there is now a site called "you might not need jquery" which breaks down - by level of IE support required - all the functionality of jquery and provides some alternative, smaller libraries.
IE8 document ready script according to you might not need jquery
function ready(fn) {
if (document.readyState != 'loading')
fn();
else if (document.addEventListener)
document.addEventListener('DOMContentLoaded', fn);
else
document.attachEvent('onreadystatechange', function() {
if (document.readyState != 'loading')
fn();
});
}
Really, if you care about Internet Explorer 9+ only, this code would be enough to replace jQuery.ready:
document.addEventListener("DOMContentLoaded", callback);
If you worry about Internet Explorer 6 and some really strange and rare browsers, this will work:
domReady: function (callback) {
// Mozilla, Opera and WebKit
if (document.addEventListener) {
document.addEventListener("DOMContentLoaded", callback, false);
// If Internet Explorer, the event model is used
} else if (document.attachEvent) {
document.attachEvent("onreadystatechange", function() {
if (document.readyState === "complete" ) {
callback();
}
});
// A fallback to window.onload, that will always work
} else {
var oldOnload = window.onload;
window.onload = function () {
oldOnload && oldOnload();
callback();
}
}
},
Cross-browser (old browsers too) and a simple solution:
var docLoaded = setInterval(function () {
if(document.readyState !== "complete") return;
clearInterval(docLoaded);
/*
Your code goes here i.e. init()
*/
}, 30);
Showing alert in jsfiddle
I was recently using this for a mobile site. This is John Resig's simplified version from "Pro JavaScript Techniques". It depends on 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;
})();
The jQuery answer was pretty useful to me. With a little refactory it fitted my needs well.
I hope it helps anybody else.
function onReady ( callback ){
var addListener = document.addEventListener || document.attachEvent,
removeListener = document.removeEventListener || document.detachEvent
eventName = document.addEventListener ? "DOMContentLoaded" : "onreadystatechange"
addListener.call(document, eventName, function(){
removeListener( eventName, arguments.callee, false )
callback()
}, false )
}
Here is the smallest code snippet to test DOM ready which works across all browsers (even IE 8):
r(function(){
alert('DOM Ready!');
});
function r(f){/in/.test(document.readyState)?setTimeout('r('+f+')',9):f()}
See this answer.
Just add this to the bottom of your HTML page...
<script>
Your_Function();
</script>
Because, HTML documents are parsed by top-bottom.
Most minimal and 100% working
I have picked the answer from PlainJS and it's working fine for me. It extends DOMContentLoaded so that it can be accepted at all the browsers.
This function is the equivalent of jQuery's $(document).ready() method:
document.addEventListener('DOMContentLoaded', function(){
// do something
});
However, in contrast to jQuery, this code will only run properly in modern browsers (IE > 8) and it won't in case the document is already rendered at the time this script gets inserted (e.g. via Ajax). Therefore, we need to extend this a little bit:
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();
});
This covers basically all possibilities and is a viable replacement for the jQuery helper.
Simplest way using pure JavaScript. Without jQuery:
document.addEventListener("DOMContentLoaded", function(event) {
// Your code to run since DOM is loaded and ready
});
It is worth looking in Rock Solid addEvent() and http://www.braksator.com/how-to-make-your-own-jquery.
Here is the code in case the site goes down
function addEvent(obj, type, fn) {
if (obj.addEventListener) {
obj.addEventListener(type, fn, false);
EventCache.add(obj, type, fn);
}
else if (obj.attachEvent) {
obj["e"+type+fn] = fn;
obj[type+fn] = function() { obj["e"+type+fn]( window.event ); }
obj.attachEvent( "on"+type, obj[type+fn] );
EventCache.add(obj, type, fn);
}
else {
obj["on"+type] = obj["e"+type+fn];
}
}
var EventCache = function(){
var listEvents = [];
return {
listEvents : listEvents,
add : function(node, sEventName, fHandler){
listEvents.push(arguments);
},
flush : function(){
var i, item;
for(i = listEvents.length - 1; i >= 0; i = i - 1){
item = listEvents[i];
if(item[0].removeEventListener){
item[0].removeEventListener(item[1], item[2], item[3]);
};
if(item[1].substring(0, 2) != "on"){
item[1] = "on" + item[1];
};
if(item[0].detachEvent){
item[0].detachEvent(item[1], item[2]);
};
item[0][item[1]] = null;
};
}
};
}();
// Usage
addEvent(window, 'unload', EventCache.flush);
addEvent(window, 'load', function(){alert("I'm ready");});
It's always good to use JavaScript equivalents as compared to jQuery. One reason is one fewer library to depend on and they are much faster than the jQuery equivalents.
One fantastic reference for jQuery equivalents is http://youmightnotneedjquery.com/.
As far as your question is concerned, I took the below code from the above link :)
Only caveat is it only works with Internet Explorer 9 and later.
function ready(fn) {
if (document.readyState != 'loading') {
fn();
}
else {
document.addEventListener('DOMContentLoaded', fn);
}
}
This cross-browser code will call a function once the DOM is ready:
var domReady=function(func){
var scriptText='('+func+')();';
var scriptElement=document.createElement('script');
scriptElement.innerText=scriptText;
document.body.appendChild(scriptElement);
};
Here's how it works:
The first line of domReady calls the toString method of the function to get a string representation of the function you pass in and wraps it in an expression that immediately calls the function.
The rest of domReady creates a script element with the expression and appends it to the body of the document.
The browser runs script tags appended to body after the DOM is ready.
For example, if you do this: domReady(function(){alert();});, the following will appended to the body element:
<script>(function (){alert();})();</script>
Note that this works only for user-defined functions. The following won't work: domReady(alert);
How about this solution?
// other onload attached earlier
window.onload=function() {
alert('test');
};
tmpPreviousFunction=window.onload ? window.onload : null;
// our onload function
window.onload=function() {
alert('another message');
// execute previous one
if (tmpPreviousFunction) tmpPreviousFunction();
};
We found a quick-and-dirty cross browser implementation of ours that may do the trick for most simple cases with a minimal implementation:
window.onReady = function onReady(fn){
document.body ? fn() : setTimeout(function(){ onReady(fn);},50);
};
I simply use:
setTimeout(function(){
//reference/manipulate DOM here
});
And unlike document.addEventListener("DOMContentLoaded" //etc as in the very top answer, it works as far back as IE9 -- http://caniuse.com/#search=DOMContentLoaded only indicates as recently as IE11.
Interestingly I stumbled upon this setTimeout solution in 2009: Is checking for the readiness of the DOM overkill?, which probably could have been worded slightly better, as I meant "is it overkill to use various frameworks' more complicated approaches to check for the readiness of the DOM".
My best explanation for why this technique works is that, when the script with such a setTimeout has been reached, the DOM is in the middle of being parsed, so execution of the code within the setTimeout gets deferred until that operation is finished.
Comparison
Here (in below snippet) is comparison of chosen available browser "built-in" methods and their execution sequence. Remarks
the document.onload (X) is not supported by any modern browser (event is never fired)
if you use <body onload="bodyOnLoad()"> (F) and at the same time window.onload (E) then only first one will be executed (because it override second one)
event handler given in <body onload="..."> (F) is wrapped by additional onload function
document.onreadystatechange (D) not override document .addEventListener('readystatechange'...) (C) probably cecasue onXYZevent-like methods are independent than addEventListener queues (which allows add multiple listeners). Probably nothing happens between execution this two handlers.
all scripts write their timestamp in console - but scripts which also have access to div write their timestamps also in body (click "Full Page" link after script execution to see it).
solutions readystatechange (C,D) are executed multiple times by browser but for different document states:
loading - the document is loading (no fired in snippet)
interactive - the document is parsed, fired before DOMContentLoaded
complete - the document and resources are loaded, fired before body/window onload
<html>
<head>
<script>
// solution A
console.log(`[timestamp: ${Date.now()}] A: Head script`) ;
// solution B
document.addEventListener("DOMContentLoaded", () => {
print(`[timestamp: ${Date.now()}] B: DOMContentLoaded`);
});
// solution C
document.addEventListener('readystatechange', () => {
print(`[timestamp: ${Date.now()}] C: ReadyState: ${document.readyState}`);
});
// solution D
document.onreadystatechange = s=> {print(`[timestamp: ${Date.now()}] D: document.onreadystatechange ReadyState: ${document.readyState}`)};
// solution E (never executed)
window.onload = () => {
print(`E: <body onload="..."> override this handler`);
};
// solution F
function bodyOnLoad() {
print(`[timestamp: ${Date.now()}] F: <body onload='...'>`);
infoAboutOnLoad(); // additional info
}
// solution X
document.onload = () => {print(`document.onload is never fired`)};
// HELPERS
function print(txt) {
console.log(txt);
if(mydiv) mydiv.innerHTML += txt.replace('<','<').replace('>','>') + '<br>';
}
function infoAboutOnLoad() {
console.log("window.onload (after override):", (''+document.body.onload).replace(/\s+/g,' '));
console.log(`body.onload==window.onload --> ${document.body.onload==window.onload}`);
}
console.log("window.onload (before override):", (''+document.body.onload).replace(/\s+/g,' '));
</script>
</head>
<body onload="bodyOnLoad()">
<div id="mydiv"></div>
<!-- this script must te at the bottom of <body> -->
<script>
// solution G
print(`[timestamp: ${Date.now()}] G: <body> bottom script`);
</script>
</body>
</html>
Nowadays you should use modules. Put your code into the default function of a module and import the function into a script element.
client.js:
export default function ()
{
alert ("test");
}
index.html:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>test</title>
</head>
<body>
<script type="module">
import main from './client.js';
main ();
</script>
</body>
</html>
Here's what I use, it's fast and covers all bases I think; works for everything except IE<9.
(() => { function fn() {
// "On document ready" commands:
console.log(document.readyState);
};
if (document.readyState != 'loading') {fn()}
else {document.addEventListener('DOMContentLoaded', fn)}
})();
This seems to catch all cases:
fires immediately if the DOM is already ready (if the DOM is not "loading", but either "interactive" or "complete")
if the DOM is still loading, it sets up an event listener for when the DOM
is available (interactive).
The DOMContentLoaded event is available in IE9 and everything else, so I personally think it's OK to use this. Rewrite the arrow function declaration to a regular anonymous function if you're not transpiling your code from ES2015 to ES5.
If you want to wait until all assets are loaded, all images displayed etc then use window.onload instead.
If you don't have to support very old browsers, here is a way to do it even when your external script is loaded with async attribute:
HTMLDocument.prototype.ready = new Promise(function(resolve) {
if(document.readyState != "loading")
resolve();
else
document.addEventListener("DOMContentLoaded", function() {
resolve();
});
});
document.ready.then(function() {
console.log("document.ready");
});
For IE9+:
function ready(fn) {
if (document.readyState != 'loading'){
fn();
} else {
document.addEventListener('DOMContentLoaded', fn);
}
}
The setTimeout/setInterval solutions presented here will only work in specific circumstances.
The problem shows up especially in older Internet Explorer versions up to 8.
The variables affecting the success of these setTimeout/setInterval solutions are:
1) dynamic or static HTML
2) cached or non cached requests
3) size of the complete HTML document
4) chunked or non chunked transfer encoding
the original (native Javascript) code solving this specific issue is here:
https://github.com/dperini/ContentLoaded
http://javascript.nwbox.com/ContentLoaded (test)
this is the code from which the jQuery team have built their implementation.
If you are loading jQuery near the bottom of BODY, but are having trouble with code that writes out jQuery(<func>) or jQuery(document).ready(<func>), check out jqShim on Github.
Rather than recreate its own document ready function, it simply holds onto the functions until jQuery is available then proceeds with jQuery as expected. The point of moving jQuery to the bottom of body is to speed up page load, and you can still accomplish it by inlining the jqShim.min.js in the head of your template.
I ended up writing this code to make moving all the scripts in WordPress to the footer, and just this shim code now sits directly in the header.