When does $(document).load() execute? [duplicate] - javascript

What are differences between
$(document).ready(function(){
//my code here
});
and
$(window).load(function(){
//my code here
});
And I want to make sure that:
$(document).ready(function(){
})
and
$(function(){
});
and
jQuery(document).ready(function(){
});
are the same.
Can you tell me what differences and similarities between them?

$(document).ready(function() {
// executes when HTML-Document is loaded and DOM is ready
console.log("document is ready");
});
$(window).load(function() {
// executes when complete page is fully loaded, including all frames, objects and images
console.log("window is loaded");
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Query 3.0 version
Breaking change: .load(), .unload(), and .error() removed
These methods are shortcuts for event operations, but had several API
limitations. The event .load() method conflicted with the ajax .load()
method. The .error() method could not be used with window.onerror
because of the way the DOM method is defined. If you need to attach
events by these names, use the .on() method, e.g. change
$("img").load(fn) to $(img).on("load", fn).1
$(window).load(function() {});
Should be changed to
$(window).on('load', function (e) {})
These are all equivalent:
$(function(){
});
jQuery(document).ready(function(){
});
$(document).ready(function(){
});
$(document).on('ready', function(){
})

document.ready is a jQuery event, it runs when the DOM is ready, e.g. all elements are there to be found/used, but not necessarily all the content.
window.onload fires later (or at the same time in the worst/failing cases) when images and such are loaded. So, if you're using image dimensions for example, you often want to use this instead.
Also read a related question:
Difference between $(window).load() and $(document).ready() functions

These three functions are the same:
$(document).ready(function(){
})
and
$(function(){
});
and
jQuery(document).ready(function(){
});
here $ is used for define jQuery like $ = jQuery.
Now difference is that
$(document).ready is jQuery event that is fired when DOM is loaded, so it’s fired when the document structure is ready.
$(window).load event is fired after whole content is loaded like page contain images,css etc.

From the jQuery API Document
While JavaScript provides the load event for executing code when a
page is rendered, this event does not get triggered until all assets
such as images have been completely received. In most cases, the
script can be run as soon as the DOM hierarchy has been fully
constructed. The handler passed to .ready() is guaranteed to be
executed after the DOM is ready, so this is usually the best place to
attach all other event handlers and run other jQuery code. When using
scripts that rely on the value of CSS style properties, it's important
to reference external stylesheets or embed style elements before
referencing the scripts.
In cases where code relies on loaded assets (for example, if the
dimensions of an image are required), the code should be placed in a
handler for the load event instead.
Answer to the second question -
No, they are identical as long as you are not using jQuery in no conflict mode.

The Difference between $(document).ready() and $(window).load() functions is that the code included inside $(window).load() will run once the entire page(images, iframes, stylesheets,etc) are loaded whereas the document ready event fires before all images,iframes etc. are loaded, but after the whole DOM itself is ready.
$(document).ready(function(){
})
and
$(function(){
});
and
jQuery(document).ready(function(){
});
There are not difference between the above 3 codes.
They are equivalent,but you may face conflict if any other JavaScript Frameworks uses the same dollar symbol $ as a shortcut name.
jQuery.noConflict();
jQuery.ready(function($){
//Code using $ as alias to jQuery
});

$(document).ready(function(e) {
// executes when HTML-Document is loaded and DOM is ready
console.log("page is loading now");
});
$(document).load(function(e) {
//when html page complete loaded
console.log("completely loaded");
});

The ready event is always execute at the only html page is loaded to the browser and the functions are executed....
But the load event is executed at the time of all the page contents are loaded to the browser for the page.....
we can use $ or jQuery when we use the noconflict() method in jquery scripts...

$(window).load is an event that fires when the DOM and all the content (everything) on the page is fully loaded like CSS, images and frames. One best example is if we want to get the actual image size or to get the details of anything we use it.
$(document).ready() indicates that code in it need to be executed once the DOM got loaded and ready to be manipulated by script. It won't wait for the images to load for executing the jQuery script.
<script type = "text/javascript">
//$(window).load was deprecated in 1.8, and removed in jquery 3.0
// $(window).load(function() {
// alert("$(window).load fired");
// });
$(document).ready(function() {
alert("$(document).ready fired");
});
</script>
$(window).load fired after the $(document).ready().
$(document).ready(function(){
})
//and
$(function(){
});
//and
jQuery(document).ready(function(){
});
Above 3 are same, $ is the alias name of jQuery, you may face conflict if any other JavaScript Frameworks uses the same dollar symbol $. If u face conflict jQuery team provide a solution no-conflict read more.
$(window).load was deprecated in 1.8, and removed in jquery 3.0

Related

Are functions inside $(document).ready available in the global scope

If I have some code like this:
jQuery(document).ready(function() {
jQuery('body').on('mouseup', '.some-div', function(e){
});
});
Is it possible to trigger the mouseup event outside the (document).ready()
with
jQuery('.some-div').mouseup();
or should I write this code
jQuery('body').on('mouseup', '.some-div', function(e){
});
as a function outside the (document).ready()?
I don't think dependency matters as much as loading order of the whole file. $(document).ready ensures that jQuery waits to execute the main function until
the page Document Object Model (DOM) is ready for JavaScript code to
execute.
Code outside this ready block might (be tried to) run before the page is actually ready. For instance, let's say this is code that's in the head of your page:
<script>
jQuery(document).ready(function() {
jQuery('body').on('mouseup', '.some-div', function(e){
});
});
jQuery('.some-div').mouseup();
</script>
The ready block will wait, as described above, but the mouseup trigger will try to fire, but it can't. The DOM isn't ready yet, which means .some-div can't be found yet - and thus, the trigger can't be activated.
To improve the chances that DOM is ready, you can try to load your jQuery before the closing </body> tag. The ready block can stay in the head, but the trigger should then move to the end of the document to improve the likelihood that the DOM is ready (which it normally should at that stage). For an interesting read on where to place script tags, also see this highly popular post.
jQuery('.some-div').mouseup(callback); writing this outside of document ready does not ensure document is ready before event is being attached to a document element. It may happen jQuery('.some-div') is not there before we are trying to access and attach an event listener.
jQuery(function() {
jQuery('body').on('mouseup', '.some-div', function(e){
});
is equivalent to
jQuery(document).ready(function() {
jQuery('body').on('mouseup', '.some-div', function(e){
});
});
Both the ways are good to ensure availability of dom elements before access.
Once the event is attached you can trigger any time. But you should always make sure document is ready.
Once .ready() is executed and event is binded, you can call it outside of that function.
Yes it's possible to trigger mouseup outside $.ready() using
jQuery('.some-div').mouseup();
But remember to call it after $.ready gets executed. In practice it requires another $.ready handler or just the invocation in the same one at the end.
Try this :
$(document).on('mouseup','.some-div',function(){
//code there
});

Why $(function(){...})?

Example 1
Example 2
...Both of these use (from what I can tell) jquery's clone on a function block, as the outermost element of the script. Why is it done this way? What would be lost if that were omitted?
P.S. Is this like instantiating an object from a class?
It is needed to call the function when the document is ready.
As of http://api.jquery.com/ready/
$(document).ready(function() {
// Handler for .ready() called.
});
Which is equivalent to calling:
$(function() {
// Handler for .ready() called.
});
that obviously is equal to
jQuery(function() {
// Your code using failsafe $ alias here...
});
here jQuery is used instead in order to not conflict with $ in case it's used by another library.
This is basically the DOMReady event. The function with your code is the code to be executed when the DOM is ready, but before all resources are loaded.
This ensures that all the HTML elements in your source code would be ready for manipulation in JS. Otherwise you may miss elements that are otherwise in your source code when trying to select them.

What's the difference between using onload in the DOM and .load() in jQuery?

For example:
<iframe onload="functionName('id-name', 'http://domain.com');"/>
versus
$('#id-name').load(functionName('id-name', "http://domain.com');
(Actually... is my jQuery right?)
UPDATE: Thanks, all, for the responses. I'm using:
$('#id-name').load(function() {
functionName('id-name', 'http://domain.com');
});
ETA: "body" was supposed to be an iframe (oops), so am not using window.load.
First of all, the syntax of your jQuery is wrong. The jQuery that's analogous would be:
$('#id-name').load(function() {
functionName('id-name', "http://domain.com');
});
To bind an event handler, you have to supply a function, you were actually calling the function at the binding time.
However, this is not equivalent for a few reasons.
First, you're binding the handler to the #id-name element, not the body (unles you also did <body id="id-name">. So it wouldn't run when the body is loaded, but only when that specific element is loaded. In general, per-element load handlers are only useful for elements that have separate sources that get loaded asynchronously (e.g. images and iframes); they allow you to detect and take action when those elements are filled in. This is particular useful if you're changing the source dynamically.
Second, ssuming your jQuery code is in the $(document).ready(...) handler, as most jQuery code is, it doesn't run until after the DOM is fully loaded. By that time, the body's onload event has already been triggered. Any handlers added at this time will not run for elements that were already loaded. I've created a fiddle that demonstrates this:
<body onload="alert('inline body onload');">
<div id="foo"></div>
</body>
$(document).ready(function () {
$("#foo").load(function () {
alert("foo onload");
});
$("body").load(function () {
alert("jquery body onload");
});
});
Only the inline body onload alert fires.
However, if you just want a jQuery equivalent to putting a function call in the <body onload=""> attribute, the $(document).ready() handler is considered analogous. See jQuery equivalent of body onLoad, the first question in the Related sidebar.
However, as Gloserio's answer says, $(window).load(...) does work, despite the timing (it's recognized specially, similar to $(document).ready()). This modified fiddle demonstrates it.
$(window).load(function () {
functionName('id-name', "http://domain.com');
});
Seems to be a fair enough equivalent of body's load event.
Related :
load event in jQuery
SOF has answered all : jQuery equivalent of body onLoad
onload is a DOM event that is triggered when the page begins to load.
.load() is a shortcut to an AJAX call using jQuery.
They really have nothing in common...other than having "load" in their names.

window.onload vs $(document).ready()

What are the differences between JavaScript's window.onload and jQuery's $(document).ready() method?
The ready event occurs after the HTML document has been loaded, while the onload event occurs later, when all content (e.g. images) also has been loaded.
The onload event is a standard event in the DOM, while the ready event is specific to jQuery. The purpose of the ready event is that it should occur as early as possible after the document has loaded, so that code that adds functionality to the elements in the page doesn't have to wait for all content to load.
window.onload is the built-in JavaScript event, but as its implementation had subtle quirks across browsers (Firefox, Internet Explorer 6, Internet Explorer 8, and Opera), jQuery provides document.ready, which abstracts those away, and fires as soon as the page's DOM is ready (doesn't wait for images, etc.).
$(document).ready (note that it's not document.ready, which is undefined) is a jQuery function, wrapping and providing consistency to the following events:
DOMContentLoaded - a newish event which fires when the document's DOM is loaded (which may be some time before the images, etc. are loaded); again, slightly different in Internet Explorer and in rest of the world
and window.onload (which is implemented even in old browsers), which fires when the entire page loads (images, styles, etc.)
$(document).ready() is a jQuery event. JQuery’s $(document).ready() method gets called as soon as the DOM is ready (which means that the browser has parsed the HTML and built the DOM tree). This allows you to run code as soon as the document is ready to be manipulated.
For example, if a browser supports the DOMContentLoaded event (as many non-IE browsers do), then it will fire on that event. (Note that the DOMContentLoaded event was only added to IE in IE9+.)
Two syntaxes can be used for this:
$( document ).ready(function() {
console.log( "ready!" );
});
Or the shorthand version:
$(function() {
console.log( "ready!" );
});
Main points for $(document).ready():
It will not wait for the images to be loaded.
Used to execute JavaScript when the DOM is completely loaded. Put event handlers here.
Can be used multiple times.
Replace $ with jQuery when you receive "$ is not defined."
Not used if you want to manipulate images. Use $(window).load() instead.
window.onload() is a native JavaScript function. The window.onload() event fires when all the content on your page has loaded, including the DOM (document object model), banner ads and images. Another difference between the two is that, while we can have more than one $(document).ready() function, we can only have one onload function.
A little tip:
Always use the window.addEventListener to add an event to window. Because that way you can execute the code in different event handlers .
Correct code:
window.addEventListener('load', function () {
alert('Hello!')
})
window.addEventListener('load', function () {
alert('Bye!')
})
Invalid code:
window.onload = function () {
alert('Hello!') // it will not work!!!
}
window.onload = function () {
alert('Bye!')
}
This is because onload is just property of the object, which is overwritten.
By analogy with addEventListener, it is better to use $(document).ready() rather than onload.
A Windows load event fires when all the content on your page is fully loaded including the DOM (document object model) content and asynchronous JavaScript, frames and images. You can also use body onload=. Both are the same; window.onload = function(){} and <body onload="func();"> are different ways of using the same event.
jQuery $document.ready function event executes a bit earlier than window.onload and is called once the DOM(Document object model) is loaded on your page. It will not wait for the images, frames to get fully load.
Taken from the following article:
how $document.ready() is different from window.onload()
$(document).ready(function() {
// Executes when the HTML document is loaded and the DOM is ready
alert("Document is ready");
});
// .load() method deprecated from jQuery 1.8 onward
$(window).on("load", function() {
// Executes when complete page is fully loaded, including
// all frames, objects and images
alert("Window is loaded");
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
The $(document).ready() is a jQuery event which occurs when the HTML document has been fully loaded, while the window.onload event occurs later, when everything including images on the page loaded.
Also window.onload is a pure javascript event in the DOM, while the $(document).ready() event is a method in jQuery.
$(document).ready() is usually the wrapper for jQuery to make sure the elements all loaded in to be used in jQuery...
Look at to jQuery source code to understand how it's working:
jQuery.ready.promise = function( obj ) {
if ( !readyList ) {
readyList = jQuery.Deferred();
// Catch cases where $(document).ready() is called after the browser event has already occurred.
// we once tried to use readyState "interactive" here, but it caused issues like the one
// discovered by ChrisS here: http://bugs.jquery.com/ticket/12282#comment:15
if ( document.readyState === "complete" ) {
// Handle it asynchronously to allow scripts the opportunity to delay ready
setTimeout( jQuery.ready );
// Standards-based browsers support DOMContentLoaded
} else if ( document.addEventListener ) {
// Use the handy event callback
document.addEventListener( "DOMContentLoaded", completed, false );
// A fallback to window.onload, that will always work
window.addEventListener( "load", completed, false );
// If IE event model is used
} else {
// Ensure firing before onload, maybe late but safe also for iframes
document.attachEvent( "onreadystatechange", completed );
// A fallback to window.onload, that will always work
window.attachEvent( "onload", completed );
// If IE and not a frame
// continually check to see if the document is ready
var top = false;
try {
top = window.frameElement == null && document.documentElement;
} catch(e) {}
if ( top && top.doScroll ) {
(function doScrollCheck() {
if ( !jQuery.isReady ) {
try {
// Use the trick by Diego Perini
// http://javascript.nwbox.com/IEContentLoaded/
top.doScroll("left");
} catch(e) {
return setTimeout( doScrollCheck, 50 );
}
// detach all dom ready events
detach();
// and execute any waiting functions
jQuery.ready();
}
})();
}
}
}
return readyList.promise( obj );
};
jQuery.fn.ready = function( fn ) {
// Add the callback
jQuery.ready.promise().done( fn );
return this;
};
Also I have created the image below as a quick references for both:
A word of caution on using $(document).ready() with Internet Explorer. If an HTTP request is interrupted before the entire document is loaded (for example, while a page is streaming to the browser, another link is clicked) IE will trigger the $(document).ready event.
If any code within the $(document).ready() event references DOM objects, the potential exists for those objects to be not found, and Javascript errors can occur. Either guard your references to those objects, or defer code which references those objects to the window.load event.
I have not been able to reproduce this problem in other browsers (specifically, Chrome and Firefox)
Events
$(document).on('ready', handler) binds to the ready event from jQuery. The handler is called when the DOM is loaded. Assets like images maybe still are missing. It will never be called if the document is ready at the time of binding. jQuery uses the DOMContentLoaded-Event for that, emulating it if not available.
$(document).on('load', handler) is an event that will be fired once all resources are loaded from the server. Images are loaded now. While onload is a raw HTML event, ready is built by jQuery.
Functions
$(document).ready(handler) actually is a promise. The handler will be called immediately if document is ready at the time of calling. Otherwise it binds to the ready-Event.
Before jQuery 1.8, $(document).load(handler) existed as an alias to $(document).on('load',handler).
Further Reading
The timing
On the function ready
An example
Promises
The removed event alias
window.onload: A normal JavaScript event.
document.ready: A specific jQuery event when the entire HTML has been loaded.
One thing to remember (or should I say recall) is that you cannot stack onloads like you can with ready. In other words, jQuery magic allows multiple readys on the same page, but you can't do that with onload.
The last onload will overrule any previous onloads.
A nice way to deal with that is with a function apparently written by one Simon Willison and described in Using Multiple JavaScript Onload Functions.
function addLoadEvent(func) {
var oldonload = window.onload;
if (typeof window.onload != 'function') {
window.onload = func;
}
else {
window.onload = function() {
if (oldonload) {
oldonload();
}
func();
}
}
}
// Example use:
addLoadEvent(nameOfSomeFunctionToRunOnPageLoad);
addLoadEvent(function() {
/* More code to run on page load */
});
Document.ready (a jQuery event) will fire when all the elements are in place, and they can be referenced in the JavaScript code, but the content is not necessarily loaded. Document.ready executes when the HTML document is loaded.
$(document).ready(function() {
// Code to be executed
alert("Document is ready");
});
The window.load however will wait for the page to be fully loaded. This includes inner frames, images, etc.
$(window).load(function() {
//Fires when the page is loaded completely
alert("window is loaded");
});
The document.ready event occurs when the HTML document has been loaded, and the window.onload event occurs always later, when all content (images, etc) has been loaded.
You can use the document.ready event if you want to intervene "early" in the rendering process, without waiting for the images to load.
If you need the images (or any other "content") ready before your script "does something", you need to wait until window.onload.
For instance, if you are implementing a "Slide Show" pattern, and you need to perform calculations based on image sizes, you may want to wait until window.onload. Otherwise, you might experience some random problems, depending on how fast the images will get loaded. Your script would be running concurrently with the thread that loads images. If your script is long enough, or the server is fast enough, you may not notice a problem, if images happen to arrive in time. But the safest practice would be allowing for images to get loaded.
document.ready could be a nice event for you to show some "loading..." sign to users, and upon window.onload, you can complete any scripting that needed resources loaded, and then finally remove the "Loading..." sign.
Examples :-
// document ready events
$(document).ready(function(){
alert("document is ready..");
})
// using JQuery
$(function(){
alert("document is ready..");
})
// window on load event
function myFunction(){
alert("window is loaded..");
}
window.onload = myFunction;
Time flies, it's ECMAScript 2021 now and IE11 is used by people less and less. The most two events in contrast are load and DOMContentLoaded.
DOMContentLoaded fires after the initial HTML document has been completely loaded and parsed.
load fires after DOMContentLoaded and the whole page has loaded,
waiting for all dependent resources to finish loading. Example of resources: scripts, stylesheets, images and iframes etc.
IMPORTANT: Synchronous scripts will pause parsing of the DOM.
Both two events can be used to determine the DOM is able to use or not. For examples:
<script>
// DOM hasn't been completely parsed
document.body; // null
window.addEventListener('DOMContentLoaded', () => {
// Now safely manipulate DOM
document.querySelector('#id');
document.body.appendChild();
});
/**
* Should be used only to detect a fully-loaded page.
*
* If you just want to manipulate DOM safely, `DOMContentLoaded` is better.
*/
window.addEventListener('load', () => {
// Safely manipulate DOM too
document.links;
});
</script>
window.onload is a JavaScript inbuilt function. window.onload trigger when the HTML page loaded. window.onload can be written only once.
document.ready is a function of the jQuery library. document.ready triggers when HTML and all JavaScript code, CSS, and images which are included in the HTML file are completely loaded.
document.ready can be written multiple times according to requirements.
When you say $(document).ready(f), you tell script engine to do the following:
get the object document and push it, since it's not in local scope, it must do a hash table lookup to find where document is, fortunately document is globally bound so it is a single lookup.
find the object $ and select it, since it's not in local scope, it must do a hash table lookup, which may or may not have collisions.
find the object f in global scope, which is another hash table lookup, or push function object and initialize it.
call ready of selected object, which involves another hash table lookup into the selected object to find the method and invoke it.
done.
In the best case, this is 2 hash table lookups, but that's ignoring the heavy work done by jQuery, where $ is the kitchen sink of all possible inputs to jQuery, so another map is likely there to dispatch the query to correct handler.
Alternatively, you could do this:
window.onload = function() {...}
which will
find the object window in global scope, if the JavaScript is optimized, it will know that since window isn't changed, it has already the selected object, so nothing needs to be done.
function object is pushed on the operand stack.
check if onload is a property or not by doing a hash table lookup, since it is, it is called like a function.
In the best case, this costs a single hash table lookup, which is necessary because onload must be fetched.
Ideally, jQuery would compile their queries to strings that can be pasted to do what you wanted jQuery to do but without the runtime dispatching of jQuery. This way you have an option of either
do dynamic dispatch of jquery like we do today.
have jQuery compile your query to pure JavaScript string that can be passed to eval to do what you want.
copy the result of 2 directly into your code, and skip the cost of eval.
window.onload is provided by DOM api and it says " the load event fires when a given resource has loaded".
"The load event fires at the end of the document loading process. At this point, all of the objects in the document are in the DOM, and all the images, scripts, links and sub-frames have finished loading."
DOM onload
But in jQuery $(document).ready() will only run once the page Document Object Model (DOM) is ready for JavaScript code to execute. This does not include images, scripts, iframes etc. jquery ready event
So the jquery ready method will run earlier than the dom onload event.

second $(document).ready event jQuery

I'm using some external jQuery with $(document).ready() to insert adverts after the document ready event has fired, something like:
$(document).ready( function() {
$('#leaderboard').html("<strong>ad code</strong>");
});
This is to prevent the UI being blocked by the slow loading of the adverts. So far it's been working well.
Now I need to insert some more ads though our CMS system, this can't be part of the external JS file, so I'm wondering can I use a second document ready event and insert it using an inline script tag? If so, what will be the order of execution the external JS document ready event first or the inline script?
You can use as many event methods as you want, jquery joins them in a queue. Order of method call is same as definition order - last added is last called.
A useful thing may be also that, you can load html code with script using ajax and when code is loaded into DOM $().ready() also will be called, so you can load ads dynamically.
Yes, adding multiple $(documents).ready()s is not a problem. All will be executed on the ready event.
Note however that your code sample is wrong. $(document).ready() takes a function, not an expression. So you should feed it a function like this:
$(document).ready( function() {
$('#leaderboard').html("<strong>ad code</strong>");
});
That function will be executed when the document is ready.
Here's a little tutorial on Multiple Document Ready
An added bonus of the jQuery way is
that you can have multiple ready()
definitions. This is the case with all
jQuery events.
$(document).ready(function () {
alert("Number One"); });
$(document).ready(function () {
alert("Number Two");
JQuery calls the ready functions in the order they are defined.
If you want to load some data first and deleay execution use holdReady().

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