How do I get Jest to recognise JQuery in my Rails project?

October 22, 2019, at 5:10 PM

I'm working on an originally-Rails-4-now-upgraded-to- app.

We originally relied on Sprockets for our JS, but have now mostly migrated to Webpacker, and for which I want to start introducing Jest tests.

We still have a residual Sprockets presence in application.js:

//= require jquery
//= require jquery_ujs
//= require select2
//= require icheck.min
//= require jquery.Jcrop.min

And in our Gemfile we require gem "jquery-rails", "~> 4.3.3"

Having recently started integrating some Vue components to the project, I want to eventually be able to test Vue components, but since I don't feel like I understand them as well as I'd like, I started out trying to test the following 'simple' bit of JQuery dom manipulation:

// PledgeFormUpdates.js
export default function() {
  window.addEventListener("load", function() {
    if ( $('#pledge-form').length == 0 ) {
    // Determine whether to show GDPR checkbox on country change
    $("#pledge_pledgor_home_country").change(function() {
      let gdpr_form_group = $("#js-gdpr-input");
      let checkbox = $('#pledge_receive_comms')
      const eu_countries = [
        "Czech Republic",
        "United Kingdom of Great Britain and Northern Ireland"
      if ( eu_countries.includes(this.value) ) {
        checkbox.prop('disabled', false);;
      } else {
        checkbox.prop('disabled', true);

The test file currently has this content:

'use strict';
import pledge_form_updates from '../../app/javascript/components/PledgeFormUpdates.js'
test('Displays GDPR checkbox on EU country selection', () => {
  // Set up our document body
  document.body.innerHTML =
    '<select id="pledge_pledgor_home_country">' +
    '  <option value="Brazil" selected>Brazil</option>'
    '  <option value="Germany">Germany</option>' +
    '  <button id="button" />' +

Our package.json includes the following config:

  // ...
  "devDependencies": {
    "jest": "^24.9.0",
    "webpack-dev-server": "^3.4.1",
    "jquery": "^3.4.1"
  "scripts": {
    "test": "jest"
  "jest": {
    "roots": [
    "setupFiles": ["./spec/javascript/setup-jest.js"]

And lastly in the setup-jest.js file, we just attempt to import JQuery, based on suggestions I saw in posts like this:

import $ from 'jquery/src/jquery';
// Other failed attempts:
// import $ from 'jquery';
// import $ from 'jquery/jquery';
global.$ = global.jQuery = $;

But all variations of this fail with some variation of the error Cannot find module 'jquery/jquery' from 'setup-jest.js'

So how can I successfully import JQuery for use in this kind of test?

ETA: Based on the comment below, in case relevant here's also the (now-amended) contents of the environment.js file:

const { environment } = require('@rails/webpacker')
const { VueLoaderPlugin } = require('vue-loader')
const vue = require('./loaders/vue')
environment.plugins.prepend('VueLoaderPlugin', new VueLoaderPlugin())
environment.loaders.prepend('vue', vue)
environment.plugins.append('Provide', new webpack.ProvidePlugin({ $: 'jquery', jQuery: 'jquery' }))
module.exports = environment
Answer 1

Ok, the answer was Cannon Moyer's comment plus one step:

From the terminal, I needed to run yarn add jquery

Then in environment.js, I needed to add his code:

environment.plugins.append('Provide', new webpack.ProvidePlugin({ $: 'jquery', jQuery: 'jquery' })) 

... and in setup-jest.js, to change import $ from 'jquery/src/jquery'; to import $ from 'jquery';

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