rails6でscriptタグのjqueryが読まれない

html.erb　のファイルでajax処理をしたくてその際scriptタグにjqueryをかきたかったのですが $ is not defined　が表示されてしまいます。素のjavasctiptは動いてくれます。

erb
1<script>
2  alert("アラート");
3</script> 
4????OK
5<script>
6  $.(window).alert("アラート");
7</script>
8ダメ
9<script>
10   document.addEventListener('turbolinks:load', function(){
11    $(function(){
12      $('window').alert();
13    });
14  });
15</script>
16 ダメ

turbolinksは切っていません。切っても動きませんでした。
application.js

js
1// This file is automatically compiled by Webpack, along with any other files
2// present in this directory. You're encouraged to place your actual application logic in
3// a relevant structure within app/javascript and only use these pack files to reference
4// that code so it'll be compiled.
5
6require("@rails/ujs").start()
7// require("turbolinks").start() 切ってみても$ is not defined
8require("@rails/activestorage").start()
9require("channels")
10require('jquery');
11
12
13// Uncomment to copy all static images under ../images to the output folder and reference
14// them with the image_pack_tag helper in views (e.g <%= image_pack_tag 'rails.png' %>)
15// or the `imagePath` JavaScript helper below.
16//
17const images = require.context('../images', true)
18// const imagePath = (name) => images(name, true)
19
20import '../stylesheets/application'
21// import './bootstrap_custom.js'
22import './hello.js'
23import './deviation.js'
24
25・
26・
27・

考えられる原因がわかる方いらっしゃいましたら助けてください。

解決方法

config/webpack/environment.js

js
1変更前
2const { environment } = require('@rails/webpacker')
3
4const webpack = require('webpack')
5environment.plugins.append(
6  'Provide',
7  new webpack.ProvidePlugin({
8    $: 'jquery',
9    jQuery: 'jquery',
10    Popper: ['popper.js', 'default']
11  })
12)
13module.exports = environment
14
15変更後
16const { environment } = require('@rails/webpacker')
17
18const webpack = require('webpack')
19environment.plugins.append(
20  'Provide',
21  new webpack.ProvidePlugin({
22    $: 'jquery/src/jquery',
23    jQuery: 'jquery/src/jquery',
24    Popper: ['popper.js', 'default']
25  })
26)
27module.exports = environment
28