jQuery

jQuery is a JavaScript library designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax.[3] It is free, open-source software using the permissive MIT License.[4] As of May 2019, jQuery is used by 73% of the 10 million most popular websites.[5] Web analysis indicates that it is the most widely deployed JavaScript library by a large margin, having at least 3 to 4 times more usage than any other JavaScript library.[5][6]

jQuery
Original author(s)John Resig
Developer(s)The jQuery Team
Initial releaseAugust 26, 2006 (2006-08-26)
Stable release
3.5.1 / (May 4, 2020 (2020-05-04))[1]
Repository
Written inJavaScript
PlatformSee § Browser support
Size27–274 KB[2]
TypeJavaScript library
LicenseMIT
Websitejquery.com

jQuery's syntax is designed to make it easier to navigate a document, select DOM elements, create animations, handle events, and develop Ajax applications. jQuery also provides capabilities for developers to create plug-ins on top of the JavaScript library. This enables developers to create abstractions for low-level interaction and animation, advanced effects and high-level, themeable widgets. The modular approach to the jQuery library allows the creation of powerful dynamic web pages and Web applications.

The set of jQuery core features—DOM element selections, traversal and manipulation—enabled by its selector engine (named "Sizzle" from v1.3), created a new "programming style", fusing algorithms and DOM data structures. This style influenced the architecture of other JavaScript frameworks like YUI v3 and Dojo, later stimulating the creation of the standard Selectors API.[7] Later, this style has been enhanced with a deeper algorithm-data fusion in an heir of jQuery, the D3.js framework.

Microsoft and Nokia bundle jQuery on their platforms.[8] Microsoft includes it with Visual Studio[9] for use within Microsoft's ASP.NET AJAX and ASP.NET MVC frameworks while Nokia has integrated it into the Web Run-Time widget development platform.[10]

Overview

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 an 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.

History

jQuery was originally created in January 2006 at BarCamp NYC by John Resig, influenced by Dean Edwards' earlier cssQuery library.[11][12] It is currently maintained by a team of developers led by Timmy Willison (with the jQuery selector engine, Sizzle, being led by Richard Gibson).[13]

jQuery was originally licensed under the CC BY-SA 2.5, and relicensed to the MIT license in 2006.[14] At the end of 2006, it was dual-licensed under GPL and MIT licenses.[15] As this led to some confusion, in 2012 the GPL was dropped and is now only licensed under the MIT license.[16]

Popularity
  • In 2015, jQuery was used on 62.7% of the top 1 million websites (according to BuiltWith), and 17% of all Internet websites.[17]
  • In 2017, jQuery was used on 69.2% of the top 1 million websites (according to Libscore).[6]
  • In 2018, jQuery was used on 78% of the top 1 million websites.[18]
  • In 2019, jQuery was used on 80% of the top 1 million websites (according to BuiltWith),[18] and 74.1% of the top 10 million (per W3Techs).[5]
  • As of Feb 2020, jQuery is used by 74.4% of the top 10 million websites (according to W3Techs).[19]

Features

jQuery includes the following features:

  • DOM element selections using the multi-browser open source selector engine Sizzle, a spin-off of the jQuery project[20]
  • 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 older browsers, such as jQuery.inArray() and jQuery.each().
  • Cross-browser support

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.[21]

Distribution

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.[22] Google in Google Hosted Libraries service and Microsoft host the library as well.[23][24]

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

<script src="jquery-3.5.1.min.js"></script>

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

<script
  src="https://code.jquery.com/jquery-3.5.1.min.js"
  integrity="sha256-9/aliU8dGd2tb6OSsuzixeV4y/faTqgFtohetphbbj0="
  crossorigin="anonymous"></script>

Interface

Functions

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 $.[25] All functions can be accessed through either of these two names.

jQuery methods

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 of class test. This node set can be manipulated by calling methods on the returned jQuery object.

Static utilities

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.

No-conflict mode

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.[26]

Typical start-point

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.[27]

Chaining

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 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.

Creating new DOM elements

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 value "VAG" and label "Volkswagen", which is then appended to the select menu:

$('select#car-brands')
  .append($('<option>')
    .attr({ value: 'VAG' })
    .text('Volkswagen')
  );

Ajax

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 plug-ins

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[28] 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.[28] The plugins in this subdomain, however, were accidentally deleted in December 2011 in an attempt to rid the site of spam.[29] The new site is a GitHub-hosted repository, which required developers to resubmit their plugins and to conform to new submission requirements.[30] jQuery provides a "Learning Center" that can help users understand JavaScript and get started developing jQuery plugins.[31]

In order to create these plug-ins, developers can either choose to write their own code from scratch or build on top of an existing structure such as the jQuery Boilerplate.

Release history
Version Initial release Latest update Minified size (KB) Additional notes
1.0 August 26, 2006 (2006-08-26) First stable release
1.1 January 14, 2007 (2007-01-14)
1.2 September 10, 2007 (2007-09-10) 1.2.6 54.5
1.3 January 14, 2009 (2009-01-14) 1.3.2 55.9 Sizzle Selector Engine introduced into core
1.4 January 14, 2010 (2010-01-14) 1.4.4 76.7
1.5 January 31, 2011 (2011-01-31) 1.5.2 83.9 Deferred callback management, ajax module rewrite
1.6 May 3, 2011 (2011-05-03) 1.6.4 89.5 Significant performance improvements to the attr() and val() functions
1.7 November 3, 2011 (2011-11-03) 1.7.2 (March 21, 2012 (2012-03-21)) 92.6 New Event APIs: .on() and .off(), while the old APIs are still supported.
1.8 August 9, 2012 (2012-08-09) 1.8.3 (November 13, 2012 (2012-11-13)) 91.4 Sizzle Selector Engine rewritten, improved animations and $(html, props) flexibility.
1.9 January 15, 2013 (2013-01-15) 1.9.1 (February 4, 2013 (2013-02-04)) 90.5 Removal of deprecated interfaces and code cleanup
1.10 May 24, 2013 (2013-05-24) 1.10.2 (July 3, 2013 (2013-07-03)) 90.9 Incorporated bug fixes and differences reported from both the 1.9 and 2.0 beta cycles
1.11 January 24, 2014 (2014-01-24) 1.11.3 (April 28, 2015 (2015-04-28)) 93.7
1.12 January 8, 2016 (2016-01-08) 1.12.4 (May 20, 2016 (2016-05-20)) 94.9
2.0 April 18, 2013 (2013-04-18) 2.0.3 (July 3, 2013 (2013-07-03)) 81.7 Dropped IE 6–8 support for performance improvements and reduction in filesize
2.1 January 24, 2014 (2014-01-24) 2.1.4 (April 28, 2015 (2015-04-28)) 82.4
2.2 January 8, 2016 (2016-01-08) 2.2.4 (May 20, 2016 (2016-05-20)) 83.6
3.0 June 9, 2016 (2016-06-09)[32] 3.0.0 (June 9, 2016 (2016-06-09)) 84.3 Promises/A+ support for Deferreds, $.ajax and $.when, .data() HTML5-compatible
3.1 July 7, 2016 (2016-07-07) 3.1.1 (September 23, 2016 (2016-09-23)) 84.7 jQuery.readyException added, ready handler errors are now not silenced
3.2 March 16, 2017 (2017-03-16)[33] 3.2.1 (March 20, 2017 (2017-03-20)) 84.6 Added support for retrieving contents of <template> elements, and deprecation of various old methods.
3.3 January 19, 2018 (2018-01-19)[34] 3.3.1 (January 20, 2018 (2018-01-20))[35] 84.9 Deprecation of old functions, functions that accept classes now also support them in array format.
3.4 April 10, 2019 (2019-04-10)[36] 3.4.1 (May 1, 2019)[37] 86.1 Performance improvements, nonce and nomodule support, fixes for radio elements, a minor security fix.
3.5 April 10, 2020 (2020-04-10)[1] 3.5.1 (May 4, 2020)[38] 87.4 Security fixes, .even() & .odd() methods, jQuery.trim deprecated

Testing framework

QUnit is a test automation framework used to test the jQuery project. The jQuery team developed it as an in-house unit testing library.[39] The jQuery team uses it to test its code and plugins, but it can test any generic JavaScript code, including server-side JavaScript code.[39]

As of 2011, the jQuery Testing Team uses QUnit with TestSwarm to test each jQuery codebase release.[40]

See also

References
  1. "jQuery 3.5.0 Released!". jQuery Blog. 2020-04-10. Retrieved 2020-04-11.
  2. "Open-source Libraries and File Sizes - PageCDN". pagecdn.com. Retrieved 2020-07-21.
  3. "jQuery: The write less, do more, JavaScript library". The jQuery Project. Retrieved 29 April 2010.
  4. "jQuery Project License". jQuery Foundation. Retrieved 2017-03-11.
  5. "Usage of JavaScript libraries for websites". W3Techs. Archived from the original on 2019-11-15. Retrieved 2019-11-15. jQuery (74.1%) is 3.7 times more popular than Bootstrap (19.9%).
  6. "Libscore". Archived from the original on 2017-02-19. Retrieved 2017-02-11. Top scripts are 1. jQuery (692,981 sites); 2. jQuery UI (193,680 sites); 3. Facebook SDK (175,369 sites); 4. Twitter Bootstrap JS (158,288 sites); 5. Modernizr (155,503 sites).
  7. "Selectors API Level 1, W3C Recommendation" (21 February 2013). This standard turned what was jQuery "helper methods" into JavaScript-native ones, and the wide use of jQuery stimulated the fast adoption of querySelector/querySelectorAll into main Web browsers.
  8. Resig, John (2008-09-28). "jQuery, Microsoft, and Nokia". jQuery Blog. jQuery. Retrieved 2009-01-29.
  9. Guthrie, Scott (2008-09-28). "jQuery and Microsoft". ScottGu's Blog. Retrieved 2019-04-15.
  10. "Guarana UI: A jQuery Based UI Library for Nokia WRT". Forum Nokia. Archived from the original on 2011-08-16. Retrieved 2010-03-30.
  11. York, Richard (2009). Beginning JavaScript and CSS Development with jQuery. Wiley. p. 28. ISBN 978-0-470-22779-4.
  12. Resig, John (2007-10-31). "History of jQuery". Retrieved 2019-04-15.
  13. "The jQuery Team". jquery.com. JS Foundation. Retrieved 2019-05-22. Team: Timmy Willison (jQuery Core Lead), Richard Gibson (Sizzle Lead, jQuery Core).
  14. jquery-under-the-mit-license on jquery.org (2006)
  15. license on jquery.org (archived 2010)
  16. jquery-licensing-changes on jquery.org (2012)
  17. "Handling 15,000 requests per second: The Growth Behind jQuery". www.maxcdn.com. MaxCDN. 20 June 2015. Retrieved 2018-07-02.
  18. "jQuery Usage Statistics (Dec 2019)". trends.builtwith.com. 2019-12-31. Archived from the original on 2020-02-21. Retrieved 2020-02-21.
  19. "Usage Statistics and Market Share of JavaScript Libraries (February 2020)". W3Techs. 2020-02-21. Archived from the original on 2020-02-21. Retrieved 2020-02-21.
  20. Resig, John (2009-01-14). "jQuery 1.3 and the jQuery Foundation". jQuery Blog. Retrieved 2009-05-04.
  21. Browser Support | jQuery
  22. jquery.org, jQuery Foundation -. "jQuery CDN".
  23. "Google Libraries API - Developer's Guide". Retrieved March 11, 2012.
  24. "Microsoft Ajax Content Delivery Network". ASP.net. Microsoft Corporation. Retrieved 2019-04-15.
  25. js.foundation, JS Foundation -. "jQuery() | jQuery API Documentation". api.jquery.com. Retrieved 2018-07-02.
  26. "jQuery.noConflict() jQuery API Documentation".
  27. jquery.org, jQuery Foundation -. "jQuery Core 3.0 Upgrade Guide - jQuery".
  28. "Plugins". The jQuery Project. Retrieved 2019-04-15.
  29. "What Is Happening To The jQuery Plugins Site?". jQuery Blog. Retrieved 22 April 2015.
  30. "jquery/plugins.jquery.com". GitHub. Retrieved 22 April 2015.
  31. "jQuery Learning Center". jQuery Foundation. Retrieved 2014-07-02.
  32. Chesters, James (2016-06-15). "Long-awaited jQuery 3.0 Brings Slim Build". infoq.com. Retrieved 2017-01-28.
  33. "jQuery 3.2.0 Is Out!". jQuery Blog. 16 March 2017. Retrieved 12 March 2018.
  34. "jQuery 3.3.0 – A fragrant bouquet of deprecations and…is that a new feature?". jQuery Blog. 2018-01-19. Retrieved 2019-04-15.
  35. "jQuery 3.3.1 – fixed dependencies in release tag". jQuery Blog. 2018-01-20. Retrieved 2019-04-15.
  36. "jQuery 3.4.0 Released". jQuery Blog. 2018-04-10. Retrieved 2019-04-15.
  37. "jQuery 3.4.1: triggering focus events in IE and finding root elements in iOS 10". jQuery Blog. jQuery Foundation.
  38. "jQuery 3.5.1 Released: Fixing a Regression". jQuery Blog. jQuery Foundation.
  39. "History". qunitjs.com. Retrieved 2019-04-15.
  40. "jQuery Testing Team Wiki".

Further reading
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