What jQuery does?

Introduction

The jQuery library provides a general-purpose abstraction layer for common
features, though, assist us in accomplishing the following tasks:


• Access elements in a document: Without a JavaScript library, web developers often need to write many lines of code to traverse the Document Object Model (DOM) tree and locate specific portions of an HTML document's
structure. With jQuery, developers have a robust and efficient selector
mechanism at their disposal, making it easy to retrieve the exact piece of
the document that needs to be inspected or manipulated.
$('div.content').find('p');

• Modify the appearance of a web page: CSS offers a powerful method of
influencing the way a document is rendered, but it falls short when web
browsers do not all support the same standards. With jQuery, developers
can bridge this gap, relying on the same standards support across all
browsers. In addition, jQuery can change the classes or individual style
properties applied to a portion of the document even after the page has
been rendered.
$('ul > li:first').addClass('active');

• Alter the content of a document: Not limited to mere cosmetic changes, jQuery
can modify the content of a document itself with a few keystrokes. Text can
be changed, images can be inserted or swapped, lists can be reordered, or the
entire structure of the HTML can be rewritten and extended—all with a single
easy-to-use Application Programming Interface (API).
$('#container').append('<a href="more.html">more</a>');

• Respond to a user's interaction: Even the most elaborate and powerful
behaviors are not useful if we can't control when they take place. The jQuery
library offers an elegant way to intercept a wide variety of events, such as a
user clicking on a link, without the need to clutter the HTML code itself with
event handlers. At the same time, its event-handling API removes browser
inconsistencies that often plague web developers.
$('button.show-details').click(function() 
{
$('div.details').show();
});
 
• Animate changes being made to a document: To effectively implement such
interactive behaviors, a designer must also provide visual feedback to the
user. The jQuery library facilitates this by providing an array of effects such
as fades and wipes, as well as a toolkit for crafting new graphic displays.
$('div.details').slideDown();

• Retrieve information from a server without refreshing a page: This code
pattern has become known as Ajax, which originally stood for asynchronous
JavaScript and XML, but has since come to represent a much greater set of
technologies for communicating between the client and the server. The jQuery
library removes the browser-specific complexity from this responsive, featurerich process, allowing developers to focus on the server-end functionality.
$('div.details').load('more.html #content');

• Simplify common JavaScript tasks: In addition to all of the document-specific
features of jQuery, the library provides enhancements to basic JavaScript
constructs such as iteration and array manipulation.
$.each(obj, function(key, value)
 {
total += value;
});