Uncaught ReferenceError: $ is not defined?

Matthew C.

—March 15, 2023

The ProblemThe Problem

Say you use the global jQuery variable ($) to check if a form checkbox input is checked:

const isItemChecked = $('#itemInput').is(':checked');

And you get the following error:

Uncaught ReferenceError: $ is not defined

This is a JavaScript error that occurs when you try to access a variable or call a function that has not been defined. Why is $ not defined?

The SolutionThe Solution

The jQuery library attaches the global variables jQuery and $ to the browser window. The $ variable is the same as the jQuery variable; it’s a shortened alias for simplicity.

When the jQuery library has not been added to your application, $ will be undefined. Here are two common fixes: one for when you download the jQuery library from a CDN and one for when you get the jQuery library from npm.

Add jQuery library script from CDN before your app scriptAdd jQuery library script from CDN before your app script

The jQuery global variable $ will be undefined if you import the jQuery library using a script tag that’s added after the script tag for your application code, which uses the $ variable:

<script src="myApp.js"></script>
<script src="https://cdn.jsdelivr.net/npm/jquery@3.6.4/dist/jquery.min.js"></script>

To fix this, import the jQuery library first:

<script src="https://cdn.jsdelivr.net/npm/jquery@3.6.4/dist/jquery.min.js"></script>
<script src="myApp.js"></script>

Be sure that the URL path to the jQuery library is correct and that the library is downloaded.

Import $ from the jQuery npm libraryImport $ from the jQuery npm library

If you are using the jQuery npm package, make sure that you import the jQuery global variable ($) before using it:

import $ from 'jquery';