Installing Bootstrap in Symfony 4 with encore - symfony

Question

I tried to follow instructions from documentation but it doesn't work.
Documentation: https://symfony.com/doc/current/frontend/encore/simple-example.html
The code I have:
assets/js/app.js
require('./assets/css/app.scss');
const $ = require('jquery');
in webpackconfig
.setOutputPath('public/build/')
.setPublicPath('/build')
.addEntry('js', './assets/js/app.js')
.enableSassLoader()
.autoProvidejQuery()
const $ = require('jquery');
base.html.twig
{% block stylesheets %}
<link rel="stylesheet" href="{{ asset('build/app.scss') }}">
<link rel="stylesheet" href="{{ asset('~/bootstrap/css/bootstrap.css') }}">
{% endblock %}
And the error message in my console
127.0.0.1/:7 GET http://127.0.0.1:8000/~/bootstrap/css/bootstrap.css
net::ERR_ABORTED 404 (Not Found)
127.0.0.1/:6 GET http://127.0.0.1:8000/build/app.scss net::ERR_ABORTED 404
(Not Found)
app.js:11 Uncaught Error: Cannot find module ".assetscssapp.scss"
at webpackMissingModule (app.js:11)
at Object../assets/js/app.js (app.js:11)
at __webpack_require__ (bootstrap 63d062e87dc6edab6451:19)
at bootstrap 63d062e87dc6edab6451:62
at bootstrap 63d062e87dc6edab6451:62
Thank you !

Answer 1

The files are only created if you have run encore:
Yarn:
yarn run encore production
yarn run encore dev
yarn run encore dev --watch
Then the files can be found unter "/public/build" and asset can find them.
If you make changes to the source files, you'll have to rerun encore. On dev you can use the "-- watch" command