Definition:
jQuery is a JavaScript library that simplifies selecting and modifying web page elements, handling events, animations and asynchronous requests to the server. It provides reusable methods for common operations without having to develop each one from scratch.
It is not a different language and does not replace JavaScript: it is written in that language and is used within programs that use it.
Table of contents
How jQuery works
jQuery allows elements in a document to be selected and operations to be applied to them through its methods. It commonly uses the $() function, which can also be called as jQuery().
A selection can identify an element by its ID, class or tag type. Its text can then be modified, a class added or an action associated with an event. For example, jQuery(".notice").hide() hides elements that have the notice class.
These methods can simplify the code for certain tasks, but there is no fixed equivalence between one line of jQuery and a specific number of lines of JavaScript.
DOM, events and asynchronous requests
The DOM represents the document’s structure through objects that programs can query and modify. jQuery provides methods to traverse that structure, insert or remove elements and change attributes and content.
It also allows events to be handled, such as a click, typing in a field or submitting a form. The associated code determines what happens when each interaction occurs.
Its Ajax functions allow information to be exchanged with a server without necessarily reloading the entire page. These requests are not limited to XML: they can work with other formats, such as JSON or text.
The library also includes effects and animations. Dropdown menus, carousels and other components can be built with these functions or through plugins; not all of them are part of jQuery core.
Relationship with JavaScript and browsers
One of jQuery’s historical contributions was to provide a common interface for operations that behaved differently across browsers.
Modern browsers include native functions for many tasks that previously required more code, such as selecting elements, handling events or making requests through fetch(). As a result, using JavaScript directly may be sufficient in certain projects.
This does not automatically make an existing jQuery installation unnecessary. An application may depend on its API or on plugins developed for it. Compatibility needs to be assessed according to the version in use, the supported browsers and the project’s code.
Versions and plugins
jQuery versions may introduce behavioral changes, remove deprecated functions or stop supporting older browsers. An update does not guarantee that all existing plugins will continue to work without modifications.
For example, jQuery 4.0 removed previously deprecated functions and support for several older browsers. These changes affect compatibility and should be distinguished from minor fixes.
Plugins extend the library with additional functions. Their maintenance and compatibility depend on their respective developers, not solely on the jQuery project. jQuery UI is a related project that provides interface components, but it is not part of the core library.