Importance of jQuery

The jQuery library provides a general-purpose abstraction layer for common web scripting, and is therefore useful in almost every scripting situation. As plug?ins are constantly being developed to add new abilities. The core features, though, address the following needs:

Access parts of a page. Without a JavaScript library, many lines of code must be written to traverse the Document Object Model (DOM) tree, and locate specific portions of an HTML document's structure. jQuery offers a robust and efficient selector mechanism for retrieving exactly the piece of the document that is to be inspected or manipulated.

Modify the appearance of a 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. jQuery can bridge this gap, providing 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.

Alter the content of a page. 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 API.

Respond to a user's interaction with a page. 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.

Add animation to a page. 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 ones.

Retrieve information from a server without refreshing a page. This code pattern has become known as Asynchronous JavaScript and XML (AJAX), and assists web developers in crafting a responsive, feature-rich site. The jQuery library removes the browser-specific complexity from this process, allowing developers to focus on the server-end functionality.

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.

Why jQuery Works Well

With the recent resurgence of interest in dynamic HTML comes a proliferation of JavaScript frameworks. Some are specialized, focusing on just one or two of the above tasks. Others attempt to catalog every possible behavior and animation, and serve these all up pre-packaged. To maintain the wide range of features outlined above while remaining compact, jQuery employs several strategies:

Leverage knowledge of CSS. By basing the mechanism for locating page elements on CSS selectors, jQuery inherits a terse yet legible way of expressing a document's structure. Because a prerequisite for doing professional web development is knowledge of CSS syntax, jQuery becomes an entry point for designers who want to add behavior to their pages.

Support extensions. In order to avoid feature creep, jQuery relegates special-case uses to plug-ins. The method for creating new plug-ins is simple and well-documented, which has spurred the development of a wide variety of inventive and useful modules. Even most of the features in the basic jQuery download are internally realized through the plug-in architecture, and can be removed if desired, yielding an even smaller library.

Abstract away browser quirks. An unfortunate reality of web development is that each browser has its own set of deviations from published standards. A significant portion of any web application can be relegated to handling features differently on each platform. While the ever-evolving browser landscape makes a perfectly browser-neutral code base impossible for some advanced features, jQuery adds an abstraction layer that normalizes the common tasks, reducing the size of code, and tremendously simplifying it.

Always work with sets. When we instruct jQuery, Find all elements with the class 'collapsible' and hide them, there is no need to loop through each returned element. Instead, methods such as .hide() are designed to automatically work on sets of objects instead of individual ones. This technique, called implicit iteration, means that many looping constructs become unnecessary, shortening code considerably.

Allow multiple actions in one line. To avoid overuse of temporary variables or wasteful repetition, jQuery employs a programming pattern called chaining for the majority of its methods. This means that the result of most operations on an object is the object itself, ready for the next action to be applied to it.

These strategies have kept the jQuery package slim—roughly 20KB compressed—while at the same time providing techniques for keeping our custom code that uses the library compact, as well.

The elegance of the library comes about partly by design, and partly due to the evolutionary process spurred by the vibrant community that has sprung up around the project. Users of jQuery gather to discuss not only the development of plug?ins, but also enhancements to the core library.

Despite all of the efforts required to engineer such a flexible and robust system, the end product is free for all to use. This open-source project is dually licensed under the GNU Public License (appropriate for inclusion in many other open-source projects) and the MIT License (to facilitate use of jQuery within proprietary software).