[RUBY] [Rails 6] jQuery introduction ・ uncaught reference error $ is not defined Error solution

Development environment

• Rails 6.0.3.4
• yarn 1.22.4

table of contents

1. Introducing jQuery
2. uncaught reference error $ is not defined Error solution

1) Introducing jQuery >> Bullets

__1. Introduce jquery with yarn add jquery __ __2. Write a description to add jQuery under management to environment.js in the webpack configuration file __ __3. Write a description to call jQuery in application.js __ __4. Check if the javascript call is described in application.html.erb __

1) Introducing jQuery >> Detailed explanation

1. Introduce jquery with yarn add jquery

Terminal
$ yarn init　*Note: I don't think it is necessary if you have already installed yarn on your OS with Homebrew.
$ yarn add jquery

__ * Supplement: __ I have no problem with just "yarn add jquery", but when I checked the articles of other people, there was an explanation that "yarn init" should be entered first, so I wrote it as a supplement. Let me do it. For "Install yarn with Homebrew", the article here will be helpful.

__ * Supplement 2: __ There is also a way to write gem'jquery-rails' in the Gemfile, but Rails 6 seems to recommend yarn add. This time, we are using the Node.js package to manage it with Webpacker.

2. environment.js

app/config/webpack/environment.js

//Copy and paste this description (the original description can be deleted)
//This is the description for adding jQuery under management in the webpack configuration file.
const { environment } = require('@rails/webpacker')
const webpack = require('webpack')

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

module.exports = environment

3. application.js

app/javascript/packs/application.js

//abridgement
require("@rails/ujs").start()
require("turbolinks").start()  //I always comment out
require("@rails/activestorage").start()
require("channels")
require('jquery') //Add this
//abridgement

__ * Note: __turbolinks actively use the cache, so events that occur after the page is loaded may not work. I'm aware that it's a bit tricky to use javascript, so comment it out. (If you use the cache, the page load time will be shortened.)

4. application.html.erb ** Confirmed just in case

html.erb:app/view/layouts/application.html.erb

<!--This is what happens when you remove tourbolinks-->
<%= stylesheet_link_tag 'application', media: 'all' %>
<%= javascript_pack_tag 'application' %>

This is the flow up to the introduction of Jquery.

2) Solution for $ is not defined error

If $ is not defined, it means that jQuery has not been inserted properly, so I think that it can be solved by checking the 4 steps explained in the introduction of jQuery.

__1. Introduce jquery with yarn add jquery __ __2. Write a description to add jQuery under management to environment.js in the webpack configuration file __ __3. Write a description to call jQuery in application.js __ __4. Check if the javascript call is described in application.html.erb __

that's all.