:JQuery

jQuery, at its core, is a Document Object Model (DOM) manipulation library. The DOM is a tree-structure representation of all the elements of a Web page. jQuery simplifies the syntax for finding, selecting, and manipulating these DOM elements. For example, jQuery can be used for finding an element in the document with a certain property (e.g. all elements with the h1 tag), changing one or more of its attributes (e.g. color, visibility), or making it respond to an event (e.g. a mouse click).

jQuery also provides a paradigm for event handling that goes beyond basic DOM element selection and manipulation. The event assignment and the event callback function definition are done in a single step in a single location in the code. jQuery also aims to incorporate other highly used JavaScript functionality (e.g. fade ins and fade outs when hiding elements, animations by manipulating CSS properties).

The principles of developing with jQuery are:

• Separation of JavaScript and HTML: The jQuery library provides simple syntax for adding event handlers to the DOM using JavaScript, rather than adding HTML event attributes to call JavaScript functions. Thus, it encourages developers to completely separate JavaScript code from HTML markup.
• Brevity and clarity: jQuery promotes brevity and clarity with features like "chainable" functions and shorthand function names.
• Elimination of cross-browser incompatibilities: The JavaScript engines of different browsers differ slightly so JavaScript code that works for one browser may not work for another. Like other JavaScript toolkits, jQuery handles all these cross-browser inconsistencies and provides a consistent interface that works across different browsers.
• Extensibility: New events, elements, and methods can be easily added and then reused as a plugin.

jQuery was originally created in January 2006 at BarCamp NYC by John Resig, influenced by Dean Edwards' earlier cssQuery library.{{cite book | last=York | first=Richard | title=Beginning JavaScript and CSS Development with jQuery | page=28 | publisher=Wiley | isbn=978-0-470-22779-4 | year=2009 | url=https://books.google.com/books?id=L9otyT4crSQC&pg=PA515}}{{cite web

| url=https://www.slideshare.net/jeresig/history-of-jquery

| title=History of jQuery

| date=2007-10-31

| last=Resig|first=John

| access-date=2019-04-15}} It is currently maintained by a team of developers led by Timmy Willison (with the jQuery selector engine, Sizzle, being led by Richard Gibson).{{Cite web|url=https://jquery.org/team/|title=The jQuery Team|website=jquery.com|publisher=JS Foundation|language=en-US|access-date=2019-05-22|quote=Team: Timmy Willison (jQuery Core Lead), Richard Gibson (Sizzle Lead, jQuery Core).}}

jQuery was originally licensed under the CC BY-SA 2.5, and relicensed to the MIT License in 2006.[https://blog.jquery.com/2006/05/27/jquery-under-the-mit-license/ jquery-under-the-mit-license] on jquery.org (2006) At the end of 2006, it was dual-licensed under GPL and MIT licenses.[https://web.archive.org/web/20100301130833/http://jquery.org/license license] on jquery.org (archived 2010) As this led to some confusion, in 2012 the GPL was dropped and is now only licensed under the MIT license.{{Cite web |last= |first= |date=2012-09-10 |title=jQuery Licensing Changes |url=https://blog.jquery.com/2012/09/10/jquery-licensing-changes/ |access-date= |website=jQuery Blog |language=en}}

• In 2015, jQuery was used on 62.7% of the top 1 million websites (according to BuiltWith), and 17% of all Internet websites.{{Cite web|url=https://www.maxcdn.com/blog/maxscale-jquery/|title=Handling 15,000 requests per second: The Growth Behind jQuery|date=20 June 2015|website=www.maxcdn.com|publisher=MaxCDN|language=en-US|access-date=2018-07-02|archive-date=July 2, 2018|archive-url=https://web.archive.org/web/20180702093146/https://www.maxcdn.com/blog/maxscale-jquery/|url-status=dead}}
• In 2017, jQuery was used on 69.2% of the top 1 million websites (according to Libscore).
• In 2018, jQuery was used on 78% of the top 1 million websites.{{Cite web|url=https://trends.builtwith.com/javascript/jQuery|title=jQuery Usage Statistics (Dec 2019)|date=2019-12-31|website=trends.builtwith.com|language=en|url-status=dead|archive-url=https://web.archive.org/web/20200221204800/https://trends.builtwith.com/javascript/jQuery|archive-date=2020-02-21|access-date=2020-02-21}}
• In 2019, jQuery was used on 80% of the top 1 million websites (according to BuiltWith), and 74.1% of the top 10 million (per W3Techs).
• In 2021, jQuery was used on 77.8% of the top 10 million websites (according to W3Techs).{{Cite web|url=https://w3techs.com/technologies/overview/javascript_library|title=Usage Statistics and Market Share of JavaScript Libraries (February 2020)|date=2020-02-21|website=W3Techs|url-status=live|archive-url=https://web.archive.org/web/20200221205251/https://w3techs.com/technologies/overview/javascript_library|archive-date=2020-02-21|access-date=2020-02-21}}

jQuery includes the following features:

• DOM element selections using the multi-browser open source selector engine Sizzle, a spin-off of the jQuery project{{cite web |title=jQuery 1.3 and the jQuery Foundation |url=https://blog.jquery.com/2009/01/14/jquery-13-and-the-jquery-foundation/ |last=Resig |first=John |date=2009-01-14 |work=jQuery Blog | access-date=2009-05-04 }}
• DOM manipulation based on CSS selectors that uses elements' names and attributes, such as id and class, as criteria to select nodes in the DOM
• Events
• Effects and animations
• Ajax
• Deferred and Promise objects to control asynchronous processing
• JSON parsing
• Extensibility through plug-ins
• Utilities, such as feature detection
• Compatibility methods that are natively available in modern browsers, but need fallbacks for old browsers, such as jQuery.inArray() and jQuery.each().
• Cross-browser support

jQuery 3.0 and newer supports "current−1 versions" (meaning the current stable version of the browser and the version that preceded it) of Firefox (and ESR), Chrome, Safari, and Edge as well as Internet Explorer 9 and newer. On mobile it supports iOS 7 and newer, and Android 4.0 and newer.[//jquery.com/browser-support/ Browser Support | jQuery]

The jQuery library is typically distributed as a single JavaScript file that defines all its interfaces, including DOM, Events, and Ajax functions. It can be included within a Web page by linking to a local copy or by linking to one of the many copies available from public servers. jQuery has a content delivery network (CDN) hosted by MaxCDN.{{cite web|url=https://code.jquery.com/|title=jQuery CDN|first=jQuery Foundation -|last=jquery.org}} Google in Google Hosted Libraries service and Microsoft host the library as well.{{cite web|url=https://code.google.com/apis/ajaxlibs/documentation/#jquery |title=Google Libraries API - Developer's Guide |access-date=March 11, 2012}}{{cite web | url=https://docs.microsoft.com/en-us/aspnet/ajax/cdn/overview | title=Microsoft Ajax Content Delivery Network | publisher=Microsoft Corporation | work=ASP.net | access-date=2019-04-15}}

Example of linking a copy of the library locally (from the same server that hosts the Web page):

Example of linking a copy of the library from jQuery's public CDN:

src="https://code.jquery.com/jquery-3.5.1.min.js"

integrity="sha256-9/aliU8dGd2tb6OSsuzixeV4y/faTqgFtohetphbbj0="

crossorigin="anonymous">

jQuery provides two kinds of functions, static utility functions and jQuery object methods. Each has its own usage style.

Both are accessed through jQuery's main identifier: jQuery. This identifier has an alias named $.{{Cite web|url=https://api.jquery.com/jQuery/|title=jQuery() {{!}} jQuery API Documentation|last=js.foundation|first=JS Foundation -|website=api.jquery.com|language=en-US|access-date=2018-07-02}} All functions can be accessed through either of these two names.

The jQuery function is a factory for creating a jQuery object that represents one or more DOM nodes. jQuery objects have methods to manipulate these nodes. These methods (sometimes called commands), are chainable as each method also returns a jQuery object.

Access to and manipulation of multiple DOM nodes in jQuery typically begins with calling the $ function with a CSS selector string. This returns a jQuery object referencing all the matching elements in the HTML page. $("div.test"), for example, returns a jQuery object with all the div elements that have the class test. This node set can be manipulated by calling methods on the returned jQuery object.

These are utility functions and do not directly act upon a jQuery object. They are accessed as static methods on the jQuery or $ identifier. For example, $.ajax() is a static method.

jQuery provides a $.noConflict() function, which relinquishes control of the $ name. This is useful if jQuery is used on a Web page also linking another library that demands the $ symbol as its identifier. In no-conflict mode, developers can use jQuery as a replacement for $ without losing functionality.{{cite web|url=http://api.jquery.com/jquery.noconflict/| title=jQuery.noConflict() jQuery API Documentation}}

Typically, jQuery is used by putting initialization code and event handling functions in $(handler). This is triggered by jQuery when the browser has finished constructing the DOM for the current Web page.

$(function () {

// This anonymous function is called when the page has completed loading.

// Here, one can place code to create jQuery objects, handle events, etc.

});

or

$(fn); // The function named fn, defined elsewhere, is called when the page has loaded.

Historically, $(document).ready(callback) has been the de facto idiom for running code after the DOM is ready. However, since jQuery 3.0, developers are encouraged to use the much shorter $(handler) signature instead.{{cite web|url=https://jquery.com/upgrade-guide/3.0/#deprecated-document-ready-handlers-other-than-jquery-function|title=jQuery Core 3.0 Upgrade Guide - jQuery|first=jQuery Foundation -|last=jquery.org}}

jQuery object methods typically also return a jQuery object, which enables the use of method chains:

$('div.test')

.on('click', handleTestClick)

.addClass('foo');

This line finds all div elements with class attribute test , then registers an event handler on each element for the "click" event, then adds the class attribute foo to each element.

Certain jQuery object methods retrieve specific values (instead of modifying a state). An example of this is the val() method, which returns the current value of a text input element. In these cases, a statement such as $('#user-email').val() cannot be used for chaining as the return value does not reference a jQuery object.

Besides accessing existing DOM nodes through jQuery, it is also possible to create new DOM nodes, if the string passed as the argument to $() factory looks like HTML. For example, the below code finds an HTML select element, and creates a new option element with the value VAG and the label Volkswagen, which is then appended to the select menu:

$('select#car-brands')

.append($('')

.prop(value,"VAG")

.text('Volkswagen')

);

It is possible to make Ajax requests (with cross-browser support) with $.ajax() to load and manipulate remote data.

$.ajax({

type: 'POST',

url: '/process/submit.php',

data: {

name : 'John',

location : 'Boston',

},

}).then(function(msg) {

alert('Data Saved: ' + msg);

}).catch(function(xmlHttpRequest, statusText, errorThrown) {

alert(

'Your form submission failed.\n\n'

+ 'XML Http Request: ' + JSON.stringify(xmlHttpRequest)

+ ',\nStatus Text: ' + statusText

+ ',\nError Thrown: ' + errorThrown);

});

This example posts the data name=John and location=Boston to /process/submit.php on the server. When this request finishes the success function is called to alert the user. If the request fails it will alert the user to the failure, the status of the request, and the specific error.

The above example uses the .then() and .catch() methods to register callbacks that run when the response has completed. These promise callbacks must be used due to the asynchronous nature of Ajax requests.

jQuery's architecture allows developers to create plug-in code to extend its function. There are thousands of jQuery plug-ins available on the Web{{cite web|title=Plugins|url=https://plugins.jquery.com/|publisher=The jQuery Project|access-date=2019-04-15}} that cover a range of functions, such as Ajax helpers, Web services, datagrids, dynamic lists, XML and XSLT tools, drag and drop, events, cookie handling, and modal windows.

An important source of jQuery plug-ins is the plugins sub-domain of the jQuery Project website. The plugins in this subdomain, however, were accidentally deleted in December 2011 in an attempt to rid the site of spam.{{cite web|url=https://blog.jquery.com/2011/12/08/what-is-happening-to-the-jquery-plugins-site/#pluginstldr|title=What Is Happening To The jQuery Plugins Site?|work=jQuery Blog|access-date=22 April 2015}} The new site is a GitHub-hosted repository, which required developers to resubmit their plugins and to conform to new submission requirements.{{cite web|url=https://github.com/jquery/plugins.jquery.com|title=jquery/plugins.jquery.com|work=GitHub|access-date=22 April 2015}} jQuery provides a "Learning Center" that can help users understand JavaScript and get started developing jQuery plugins.{{cite web|title=jQuery Learning Center|url=http://learn.jquery.com/|publisher=jQuery Foundation |access-date=2014-07-02}}