jQuery – js library free!

jQuery

jQuery is a cross-platform JavaScript library designed to simplify the client-side scripting of HTML. jQuery is the most popular JavaScript library in use today, with installation on 65% of the top 10 million highest-trafficked sites on the Web. jQuery is free open-source software licensed under the MIT License.

Contents:
1 Overview
2 Features
3 Usage
    3.1 Including on a webpage
    3.2 Usage styles
    3.3 .noConflict()
    3.4 .ready()
    3.5 Chaining elements
    3.6 Creating new DOM elements
    3.7 $. – utility functions
    3.8 $.ajax
4 Plugins
5 Books

jQuery was originally released in January 2006 at BarCamp NYC by John Resig and was influenced by Dean Edwards‘ earlier cssQuery library. It is currently maintained by a team of developers led by Timmy Willison. As of 2015, jQuery remains the most widely used JavaScript library on the Web.

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 plugins 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 “Sizzle”, created a new “programming style”, fusing algorithms and DOM data structures. This style influenced the architecture of other JavaScript frameworks like YUI 3 and Dojo, later stimulating the creation of the standard Selectors API.

jQuery overview

jQuery, at its core, is a DOM manipulation library. The DOM is a tree-structure representation of all the elements of a Web page and 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 h3 tag), changing one or more of its attributes (e.g. color, visibility), or making it respond to an event (e.g. a mouse hover).

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 advantages of using jQuery are:

  • Encourages 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.
  • 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. Like other JavaScript toolkits, jQuery handles all these cross-browser inconsistencies and provides a consistent interface that works across different browsers.
  • Extensible: New events, elements, and methods can be easily added and then reused as a plugin.

jQuery 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;
  • 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 plugins;
  • Utilities, such as 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.
    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 (that accounts for under 2% of all browsers in use) and supports only IE 9 and later versions.

www.jquery.com

jQuery Usage

Including the jQuery library on a webpage

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.

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

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

<script src="https://code.jquery.com/jquery-latest.min.js"></script>

jQuery 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 jQuery 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.

Typical jQuery 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 are 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 img
	});
});

The following syntaxes are equivalent:

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

Chaining jQuery commands

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 with jQuery

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 currency, and adds an option element with value “USD” and text “US Dollar”:

$('select#currency').append($('<option />').attr({value:"USD"}).append("US Dollar"));

jQuery Utility Functions

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

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

AJAX and jQuery

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=Sergey&location=Moscow"
}).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=Segrey and location=Moscow 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.

Note that this 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 Plugins

jQuery’s architecture allows developers to create plugin code to extend its function. There are thousands of jQuery plugins available on the Web 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 plugins is the plugins subdomain 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. The new site will include a GitHub-hosted repository, which will require developers to resubmit their plugins and to conform to new submission requirements. There are alternative plugin search engines like www.jquer.in that take more specialized approaches, such as listing only plugins that meet certain criteria (e.g. those that have a public code repository). jQuery provides a “Learning Center” that can help users understand JavaScript and get started developing jQuery plugins.

www.plugins.jquery.com

jQuery books

  • Karl Swedberg – jQuery Reference Guide, 2007.
  • Karl Swedberg – Learning jQuery 1.3, 2009.
  • Leon Revill – jQuery 2.0 Development Cookbook, 2012.
  • Raymond Camden – Jquery Mobile Web Development Essentials, 2012.
  • Dan Wellman – jQuery Hotshot, 2013.
  • N. Maclees – jQuery for Designers, 2012.