- jQuery.ready() equivalent event listener on elements?
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- $( document ).ready()
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- .ready()
- version added: 1.0 .ready( handler )
- JavaScript document.ready() – Document Ready JS and jQuery Example
- How to Use the $(document).ready() Method in jQuery
- How to Use the DOMContentLoaded Event in JavaScript
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jQuery.ready() equivalent event listener on elements?
I am using jQuery JavaScript library. I like the event listener ready on $(document) that fires when the DOM is set up. ( Pretty similar to .onload but without external sources ) I would find it very useful, if there was an event listener which has a very similar behavior to this, but fires when an element is fully loaded. (f.e.: Picture, a Div with an extremely long text content, such ) I would appreciate both jQuery or JavaScript methods.
3 Answers 3
There is no event fired when an arbitrary DOM element such as a becomes ready. Images have their own load event to tell you when the image data has been loaded and has been rendered and a few other special types of elements have an event. But, regular DOM elements do not have such an event.
If you want javascript code to be executed as soon as an arbitrary DOM element is ready, the only way to do that is to place a function call in an inline script right after that DOM element. At that point that DOM element will be ready, but the rest of the DOM afterwards may not yet be ready. Otherwise, the script can be placed at the end of the document or the script can be fired when the whole document is ready.
Here are the existing load events expressed in jQuery form (these can all be done in plain JS too):
// when a particular image has finished loading the image data $("#myImage").load(fn); // when all elements in the document are loaded and ready for manipulation $(document).ready(fn); // when the DOM and all dynamically loaded resources such as images are ready $(window).load(fn); In jQuery, you can also dynamically load content and be notified when that content has been loaded using the .load() method like this:
$( "#result" ).load( "ajax/test.html", function() < alert( "Load was performed." ); >); Internally, this just does an ajax call to fetch the data and then calls the callback after the data has been retrieved by ajax and then inserted into the document. It isn’t a native event.
If you have some code that is dynamically loading elements in to the DOM and you want to know when those DOM elements are present, then the best way to know when they are ready is to have the code that adds them to the DOM create some sort of event to tell you when it’s ready. This prevents battery wasting polling efforts trying to find out if the element is now in the DOM.
It is also possible to use the DOM MutationObserver to see when specific types of changes have been made to the DOM.
$( document ).ready()
A page can’t be manipulated safely until the document is «ready.» jQuery detects this state of readiness for you. Code included inside $( document ).ready() will only run once the page Document Object Model (DOM) is ready for JavaScript code to execute. Code included inside $( window ).on( «load», function() < . >) will run once the entire page (images or iframes), not just the DOM, is ready.
// A $( document ).ready() block.$( document ).ready(function( )console.log( "ready!" );>);
Experienced developers sometimes use the shorthand $() for $( document ).ready() . If you are writing code that people who aren't experienced with jQuery may see, it's best to use the long form.
// Shorthand for $( document ).ready()$(function( )console.log( "ready!" );>);
You can also pass a named function to $( document ).ready() instead of passing an anonymous function.
// Passing a named function instead of an anonymous function.function readyFn( jQuery )// Code to run when the document is ready.>$( document ).ready( readyFn );// or:$( window ).on( "load", readyFn );
The example below shows $( document ).ready() and $( window ).on( "load" ) in action. The code tries to load a website URL in an and checks for both events:
html>head>script src="https://code.jquery.com/jquery-1.9.1.min.js"> script>script>$( document ).ready(function( )console.log( "document loaded" );>);$( window ).on( "load", function( )console.log( "window loaded" );>);script>head>body>iframe src="http://techcrunch.com"> iframe>body>html>
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.ready()
Description: Specify a function to execute when the DOM is fully loaded.
version added: 1.0 .ready( handler )
The .ready() method offers a way to run JavaScript code as soon as the page's Document Object Model (DOM) becomes safe to manipulate. This will often be a good time to perform tasks that are needed before the user views or interacts with the page, for example to add event handlers and initialize plugins. When multiple functions are added via successive calls to this method, they run when the DOM is ready in the order in which they are added. As of jQuery 3.0, jQuery ensures that an exception occuring in one handler does not prevent subsequently added handlers from executing.
Most browsers provide similar functionality in the form of a DOMContentLoaded event. However, jQuery's .ready() method differs in an important and useful way: If the DOM becomes ready and the browser fires DOMContentLoaded before the code calls .ready( handler ) , the function handler will still be executed. In contrast, a DOMContentLoaded event listener added after the event fires is never executed.
Browsers also provide the load event on the window object. When this event fires it indicates that all assets on the page have loaded, including images. This event can be watched in jQuery using $( window ).on( "load", handler ) . 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.
Note that although the DOM always becomes ready before the page is fully loaded, it is usually not safe to attach a load event listener in code executed during a .ready() handler. For example, scripts can be loaded dynamically long after the page has loaded using methods such as $.getScript() . Although handlers added by .ready() will always be executed in a dynamically loaded script, the window 's load event has already occurred and those listeners will never run.
jQuery offers several ways to attach a function that will run when the DOM is ready. All of the following syntaxes are equivalent:
- $( handler )
- $( document ).ready( handler )
- $( "document" ).ready( handler )
- $( "img" ).ready( handler )
- $().ready( handler )
As of jQuery 3.0, only the first syntax is recommended; the other syntaxes still work but are deprecated. This is because the selection has no bearing on the behavior of the .ready() method, which is inefficient and can lead to incorrect assumptions about the method's behavior. For example, the third syntax works with "document" which selects nothing. The fourth syntax waits for the document to be ready but implies (incorrectly) that it waits for images to become ready.
There is also $(document).on( "ready", handler ) , deprecated as of jQuery 1.8 and removed in jQuery 3.0. Note that if the DOM becomes ready before this event is attached, the handler will not be executed.
The .ready() method is typically used with an anonymous function:
$( document ).ready(function( )// Handler for .ready() called.>);
JavaScript document.ready() – Document Ready JS and jQuery Example
Ihechikara Vincent Abba
When working with JavaScript and the Document Object Model (DOM), you might want your script to run only when the DOM has loaded.
You can do this using the $(document).ready() method in jQuery, or the DOMContentLoaded event in vanilla JavaScript.
In this article, you'll learn how to make your JavaScript code run only when the DOM has loaded using jQuery and vanilla JavaScript.
How to Use the $(document).ready() Method in jQuery
Before JavaScript runs in the browser, it waits for the contents of the document to load. This includes stylesheets, images, and so on.
As a convention, placing the script element just before the closing body tag makes the script wait for the rest of the document to load before running.
We also can make this process faster in jQuery by using the $(document).ready() method. The $(document).ready() method only waits for the DOM to load, it doesn't wait for stylesheets, images, and iframes.
In the code above, the $(document).ready() method will only run after the DOM has loaded. So you'll only see "Hello World!" in the console after the $(document).ready() method has started running.
In summary, you can write all your jQuery code inside the $(document).ready() method. This way, your code will wait for the DOM to be loaded before running.
How to Use the DOMContentLoaded Event in JavaScript
Just like jQuery's $(document).ready() method, the DOMContentLoaded event fires once the DOM has loaded – it doesn't wait for stylesheets and images.
Here's how to use the DOMContentLoaded event:
document.addEventListener("DOMContentLoaded", () => < console.log("Hello World!"); >);Once the DOM has loaded, the DOMContentLoaded event will detect it and run.
You should use the DOMContentLoaded event when:
- You have certain functionalities in your webpage that should fire immediately without waiting for the rest of the page content.
- You have a script tag placed within the head element.
Summary
In this article, we talked about the $(document).ready() method in jQuery, and the DOMContentLoaded event in vanilla JavaScript.
We use them to execute JavaScript code when the DOM has loaded.
The interesting part of these functionalities is that they let JavaScript code run without waiting for images and stylesheets to load completely in a web page.