What are the differences between JavaScript”s window.onload and jQuery”s $(document).ready() method?
The ready event occurs after the HTML document has been loaded, while the onload event occurs later, when all content (e.g. images) also has been loaded.
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The onload event is a standard event in the DOM, while the ready event is specific to jQuery. The purpose of the ready event is that it should occur as early as possible after the document has loaded, so that code that adds functionality to the elements in the page doesn”t have to wait for all content to load.
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window.onload is the built-in JavaScript event, but as its implementation had subtle quirks across browsers (Firefox, InternetExplorer6, InternetExplorer8, and Opera), jQuery provides document.ready, which abstracts those away, and fires as soon as the page”s DOM is ready (doesn”t wait for images, etc.).
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$(document).ready (note that it”s not document.ready, which is undefined) is a jQuery function, wrapping and providing consistency to the following events:
document.ondomcontentready / document.ondomcontentloaded – 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 InternetExplorer and in rest of the worldand window.onload (which is implemented even in old browsers), which fires when the entire page loads (images, styles, etc.) Share Improve this answer Follow edited Apr 11 “16 at 21:26
Peter Mortensen 28.1k2121 gold badges9494 silver badges123123 bronze badges answered Sep 13 “10 at 6:30 Piskvor left the buildingPiskvor left the building 87.6k4343 gold badges170170 silver badges220220 bronze badges 7 | Show 2 more comments 88$(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.
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