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jQuery

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jQuery
Original author(s)John Resig
Developer(s)jQuery Team
Initial releaseAugust 26, 2006 (2006-08-26)
Stable release
1.11.2 (December 18, 2014 (2014-12-18))
2.1.3 (December 18, 2014 (2014-12-18))
Repository
Written inJavaScript
PlatformSee Browser support
Size
ver gzip prod dev
1.x 31 90.9 266
2.x 27.7 81.6 236
(KB)
TypeJavaScript library
LicenseMIT[1]
Websitejquery.com

jQuery is a cross-platform JavaScript library designed to simplify the client-side scripting of HTML.[2] Used by over 60% of the 10,000 most visited websites,[3] jQuery is the most popular JavaScript library in use today.[4][5] jQuery is free, open-source software licensed under the MIT License.[1]

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, theme-able 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.[6]

Microsoft and Nokia bundle jQuery on their platforms.[7] Microsoft includes it with Visual Studio[8] for use within Microsoft's ASP.NET AJAX framework and ASP.NET MVC Framework while Nokia has integrated it into the Web Run-Time widget development platform.[9] jQuery has also been used in MediaWiki since version 1.16.[10]

Overview

jQuery, at its core, is a DOM (Document Object Model) manipulation library. The DOM is a tree-structure representation of all the elements of a web-page and jQuery makes finding, selecting, and manipulating these DOM elements simple and convenient. 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 provides a new paradigm for event handling in JavaScript 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 functionalities (e.g. fade ins and fade outs when hiding elements, animations by manipulating CSS properties).

The advantages of using jQuery are:

  • Separates JavaScript and HTML: Instead of using HTML attributes to call JavaScript functions for event handling, jQuery can be used to handle events purely in JavaScript. Thus, the HTML elements and JavaScript can be completely separated.
  • Brevity and Clarity: jQuery promotes brevity and clarity with features like chain-able functions and shorthand function names.
  • Eliminates cross-browser incompatibilities: The JavaScript engines of different browsers differ slightly so JavaScript code that works for one browser may not work for another. jQuery handles all these cross-browser inconsistencies and provides a consistent interface that works across different browsers.
  • Extensible: jQuery makes extending the framework very simple. New events, elements, and methods can be easily added and then reused as a plugin.

The disadvantages of using jQuery are:

  • Dubious Claims: Though it allows for attaching event listeners to DOM elements and documents without HTML attributes (something offered by the DOM itself from the beginning), the practice of binding listeners by CSS selector necessarily binds the resulting script to the document (or similarly structured documents). So the HTML documents can never be completely separate from the scripts that manipulate them and jQuery's techniques magnify this issue.[11]
  • Illegible: The "shorthand" function names do not make scripts easier to read. It is the exact opposite: function names need to be long enough to indicate what they do (which lets out most of jQuery's methods). jQuery scripts do not minimize well either as virtually every line is a method call. The idea that method names should be truncated to compensate for the design is ridiculous (and leads to relatively illegible scripts).
  • Incompetent: There have been a dozen versions of jQuery since the outset, the first half dozen are unusable today due to design mistakes, misunderstandings and browser sniffing. The most recent versions are unusable in IE 8 and under, excluding many corporate users for no good reason.[12]
  • Slow: It's extremely slow compared to using the DOM (or comparable DOM scripts), which is particularly damaging for mobile users. The script is slow enough by itself and the typical usage patterns (e.g. creating and discarding jQuery objects on every line) make for incredible inefficiencies. The idea of trading developer time during development for repeated lost time for users, simply to allow for the use of untrained labor is patently absurd.[13][14][15][16]
  • Monolithic This bloated script tries to solve everything perceived to be a "bug", often creating bugs where none existed.[17] Took a full five years (ten years after the DOM specifications were published) to figure out that DOM attributes and properties could not be handled with a single function; likely due to the author's misunderstanding of HTML and XML (cited former as a subset of the latter in Pro JavaScript Techniques, a book that predates jQuery). When it was finally fixed, it fractured the code base in two, "orphaning" older versions that were rendered incompatible. Code base was fractured again a few years later when support for IE 8 and under was dropped (with little or no benefit to anyone).[18]

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[19]
  • 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 user agent information, feature detection
  • Compatibility methods that are natively available in modern browsers but need fall backs for older ones, such as inArray() and each()
  • Multi-browser (not to be confused with cross-browser) support

Browser support

Both versions 1.x and 2.x of jQuery support "current-1 versions" (meaning the current stable version of the browser and the version that preceded it) of Firefox, Google Chrome, Safari, and Opera. Version 1.x also supports Internet Explorer 6 or higher. However, jQuery version 2.x dropped Internet Explorer 6–8 support (which represents less than 28% of all browsers in use) and supports only IE 9 and later versions.[20]

Usage

Including the library

The jQuery library is a single JavaScript file containing all of its common DOM, event, effects, and Ajax functions. It can be included within a web page by linking to a local copy or to one of the many copies available from public servers. jQuery has a CDN hosted by MaxCDN[21] (moved from MediaTemple[22] and, before that, Amazon[23]). Google[24] and Microsoft[25] host it as well. 

<script src="jquery.js"></script>

It is also possible to include jQuery directly from content delivery networks. 

<script src="http://code.jquery.com/jquery-1.11.1.min.js"></script>

Usage styles

jQuery has two usage styles:

  • Via the $ function, which is a factory method for the jQuery object. These functions, often called commands, are chainable as they all return jQuery objects.
  • Via $.-prefixed functions. These are utility functions, which do not act upon the jQuery object directly.

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 or on the nodes themselves.

No-Conflict Mode

jQuery also includes .noConflict() mode, which relinquishes control of $. This can be helpful if jQuery is used with other libraries that also use $ as an identifier. In no-conflict mode, developers can use jQuery as a replacement for $ without losing functionality.[26]

Typical start-point

The typical jQuery usage is to put initialization code and event handling functions in .ready(). This is triggered when the browser has constructed the DOM and sends a load event. 

<script type="text/javascript">
$(document).ready(function(){
        // jQuery code, event handling callbacks here
});
</script>

Callback functions for event handling are also included inside .ready() as anonymous functions but called when the event for the callback is triggered. For example, the following jQuery code adds an event handler for a mouse click on an img image element. 

$(document).ready(function(){
        $('img').click ( function() { 
              // handle the click event on any img element in the page
        });
});

The following syntaxes are equivalent:

  • $(document).ready(handler)
  • $(handler)

Chaining

Each jQuery command returns a jQuery object, so commands can be chained: 

$("div.test").add("p.quote").addClass("blue").slideDown("slow");

This line finds the union of all div tags with class attribute test and all p tags with class attribute quote, adds the class attribute blue to each matched element, and then increases their height with an animation. The $ and add functions affect the matched set, while the addClass and slideDown affect the referenced nodes.

Creating new DOM elements

Besides accessing DOM nodes through jQuery object hierarchy, it is also possible to create new DOM elements if a string passed as the argument to $() looks like HTML. For example, this line finds an HTML select element with ID carmakes, and adds an option element with value "VAG" and text "Volkswagen": 

$('select#carmakes').append($('<option />').attr({value:"VAG"}).append("Volkswagen"));

Utility Functions

Functions prefixed with $. are utility functions or functions that affect global properties and behaviour. The following, for example, is a function used for iterating over arrays called each in jQuery: 

$.each([1,2,3], function() {
  console.log(this + 1);
});

This writes "2", "3", "4" to the console.

AJAX

It is possible to perform browser-independent Ajax queries using $.ajax and associated methods to load and manipulate remote data. 

$.ajax({
  type: "POST",
  url: "example.php",
  data: "name=John&location=Boston"
}).done( function(msg) {
  alert( "Data Saved: " + msg );
}).fail( 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 example.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.

Asynchronous

Note that the above example uses the deferred nature of $.ajax() to handle its asynchronous nature: .done() and .fail() create callbacks that run only when the asynchronous process is complete.

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[27] 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 subdomain of the jQuery Project website.[27] The plugins in this subdomain, however, were accidentally deleted in December 2011 in an attempt to rid the site of spam.[28] The new site will include a GitHub-hosted repository, which will require developers to resubmit their plugins and to conform to new submission requirements.[29] There are alternative plug-in search engines[30][31] like jquer.in that take more specialized approaches, such as listing only plug-ins that meet certain criteria (e.g. those that have a public code repository). jQuery provides a "Learning Center" which can help users understand JavaScript and get started developing jQuery plugins.[32]

History

jQuery was originally released in January 2006 at BarCamp NYC by John Resig and was influenced by Dean Edwards' earlier cssQuery library.[33] It is currently maintained by a team of developers led by Dave Methvin.

Release history

Version number Release date Latest update Size Prod (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)
1.3 January 14, 2009 (2009-01-14) 55.9 Sizzle Selector Engine introduced into core
1.4 January 14, 2010 (2010-01-14)
1.5 January 31, 2011 (2011-01-31) Deferred callback management, ajax module rewrite
1.6 May 3, 2011 (2011-05-03) Significant performance improvements to the attr() and val() functions
1.7 November 3, 2011 (2011-11-03) New Event APIs: .on() and .off(), while the old APIs are still supported.
1.8 August 9, 2012 (2012-08-09) 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))[34] Removal of deprecated interfaces and code cleanup
1.10 May 24, 2013 (2013-05-24) 1.10.2 (July 3, 2013 (2013-07-03)) Incorporated bug fixes and differences reported from both the 1.9 and 2.0 beta cycles
1.11 January 24, 2014 (2014-01-24) 1.11.2 (December 18, 2014 (2014-12-18)) 93.5
2.0 April 18, 2013 (2013-04-18) 2.0.3 (July 3, 2013 (2013-07-03)) 81.1 Dropped IE 6–8 support for performance improvements and reduction in filesize
2.1 January 24, 2014 (2014-01-24) 2.1.3 (December 18, 2014 (2014-12-18)) 82.2

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.[35] The jQuery team uses it to test its code and plugins but it can test any generic JavaScript code, including server-side JavaScript code.[35]

As of 2011, the jQuery Testing Team uses QUnit with TestSwarm to test each jQuery codebase release.[36]

See also

References

  1. ^ a b "License - jQuery Project". jQuery Foundation. Retrieved 2014-07-02.
  2. ^ "jQuery: The write less, do more, JavaScript library". The jQuery Project. Retrieved 29 April 2010.
  3. ^ "JavaScript libraries usage statistics", Analysis by SimilarTech
  4. ^ "jQuery Usage Statistics". Retrieved 2013-05-17.
  5. ^ "Usage of JavaScript libraries for websites". W3Techs. Retrieved 2010-07-08.
  6. ^ "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 adption of querySelector/querySelectorAll into main web-browsers.
  7. ^ Resig, John (2008-09-28). "jQuery, Microsoft, and Nokia". jQuery Blog. jQuery. Retrieved 2009-01-29.
  8. ^ Guthrie, Scott (2008-09-28). "jQuery and Microsoft". ScottGu's Blog. Retrieved 2009-01-29.
  9. ^ "Guarana UI: A jQuery Based UI Library for Nokia WRT". Forum Nokia. Retrieved 2010-03-30.
  10. ^ "jQuery". MediaWiki. January 19, 2012. Retrieved March 11, 2012.
  11. ^ "Unrealistic JS".
  12. ^ "Thoughts on jQuery 2.0".
  13. ^ "Adding and Removing Listeners Part 2".
  14. ^ "Get Elements By Tag Name".
  15. ^ "Setting Inner HTML of a DIV".
  16. ^ "SlickSpeed Selectors Test".
  17. ^ "Deconstructing jQuery".
  18. ^ "Thoughts on jQuery 2.0".
  19. ^ Resig, John (2009-01-14). "jQuery 1.3 and the jQuery Foundation". jQuery Blog. Retrieved 2009-05-04.
  20. ^ Browser Support | jQuery
  21. ^ "jQuery CDN" – http://code.jquery.com/
  22. ^ "replace (mt) with maxcdn on pages/download.md". August 7, 2013. Retrieved December 6, 2013.
  23. ^ "CloudFront CDN for jQuery", November 19th, 2008 by John Resig, blog.jquery.com
  24. ^ "Google Libraries API - Developer's Guide". code.google.com. Retrieved March 11, 2012.
  25. ^ "Microsoft Ajax Content Delivery Network". ASP.net. Microsoft Corporation. Retrieved June 19, 2012.
  26. ^ http://api.jquery.com/jquery.noconflict/. {{cite web}}: External link in |website= (help); Missing or empty |title= (help); Missing or empty |url= (help)
  27. ^ a b "Plugins". The jQuery Project. Retrieved 26 August 2010.
  28. ^ http://blog.jquery.com/2011/12/08/what-is-happening-to-the-jquery-plugins-site/#pluginstldr
  29. ^ https://github.com/jquery/plugins.jquery.com
  30. ^ "jQuery Plugins Search". Retrieved 13 September 2012.
  31. ^ Kanakiya, Jay. "jquery plugins".
  32. ^ "jQuery Learning Center". jQuery Foundation. Retrieved 2014-07-02.
  33. ^ York, Richard (2009). Beginning JavaScript and CSS Development with jQuery. Wiley. p. 28. ISBN 978-0-470-22779-4.
  34. ^ http://blog.jquery.com/2013/02/04/jquery-1-9-1-released
  35. ^ a b "History". qunitjs.com. Retrieved 2014-07-02.
  36. ^ jQuery Testing Team Wiki http://jquerytesting.pbworks.com/w/page/41556026/FrontPage

Further reading

Wikimedia Commons has media related to JQuery.
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