Features Excluded from the jQuery Slim Build

The jQuery slim build is a lightweight distribution of the popular JavaScript library designed to reduce file size and optimize page load performance. By omitting legacy modules and features that modern web browsers natively handle, this streamlined version helps developers reduce overall bundle size. This article outlines the specific modules excluded from the jQuery slim build, what functional methods are missing as a result, and how these omissions affect development.

1. The Ajax Module

The most significant exclusion from the slim build is the entire Ajax module. In standard jQuery, the Ajax module handles asynchronous HTTP requests, data serialization, and response handling. Because modern web browsers feature the native fetch() API and XMLHttpRequest, this module is often redundant.

Methods excluded under the Ajax module include:

  • Low-Level Requests: jQuery.ajax(), jQuery.ajaxSetup(), and jQuery.ajaxPrefilter().
  • Shorthand Methods: jQuery.get(), jQuery.post(), jQuery.getJSON(), and jQuery.getScript().
  • DOM Loading: $(selector).load().
  • Form Serialization: $(form).serialize() and $(form).serializeArray().
  • Global Ajax Events: ajaxStart(), ajaxStop(), ajaxComplete(), ajaxError(), ajaxSuccess(), and ajaxSend().

If your application relies on jQuery to fetch data from an API or submit forms asynchronously without page reloads, you must handle those requests using vanilla JavaScript (fetch) or an external library like Axios.

2. The Effects Module

The slim build completely strips out the Effects (animation) module. Standard jQuery uses JavaScript-based intervals to animate CSS properties, fade elements, or slide containers. Modern web development generally favors CSS transitions and CSS animations due to superior hardware acceleration and performance.

Methods excluded under the Effects module include:

  • Custom Animations: $(selector).animate(), stop(), delay(), and finish().
  • Fading Effects: fadeIn(), fadeOut(), fadeTo(), and fadeToggle().
  • Sliding Effects: slideDown(), slideUp(), and slideToggle().
  • Display Toggling with Duration: Passing a duration or easing parameter to show(), hide(), or toggle() (e.g., show(400) or hide("slow")). Note that basic instant toggling without animations (.show() and .hide()) remains supported.
  • Configuration: jQuery.fx.off and jQuery.fx.interval.

3. Deprecated Code and Utilities

In addition to the primary modules, the slim build excludes several deprecated internal utilities that were previously retained only for backwards compatibility. This includes older animation queues and utility functions closely tied to the Ajax and Effects pipelines.

What Remains in the Slim Build?

The slim build preserves the essential core of jQuery, making it suitable for projects that only require DOM manipulation and event management. Features that remain fully intact include:

  • Core and Selectors: Element selection via the Sizzle engine ($( "div.class" )).
  • DOM Manipulation: Inserting, removing, cloning, and altering elements (append(), remove(), html(), text(), attr(), prop(), val()).
  • DOM Traversal: Moving through the document tree (find(), parent(), children(), closest(), siblings()).
  • Event Handling: Attaching and triggering events (on(), off(), trigger(), hover(), and click handlers).
  • Data and Callbacks: Managing element-specific data via .data() and utilizing Deferred/Promise objects.