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Installing Encore

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Hiya guys! And welcome to our tutorial on Webpack Encore! I have to admit, this tutorial is near and dear to my heart, because I helped write Webpack Encore. But also because I think you're going to love working with it and I know that it's going to drastically improve the way you write JavaScript.

Basically, Encore is a wrapper around Webpack... because honestly, Webpack - while amazing - is a pain to setup. And what does Webpack do? We'll get to that.

Setting up the Project

And when we do.... you're definitely going to want to code along with me. Because, we're going to code JavaScript... dramatic pause... correctly!

Download the course code from this page. After you unzip it, you'll find a start/ directory that has the same code you see here. Follow the file to get setup details and, of course, a Haiku about Webpack.

The last step will be to find a terminal, move into the project, and run:

php bin/console server:run

to start the built-in web server. Find your most favorite browser and go to: http://localhost:8000.

Aw yea, it's Lift Stuff! Our startup for keeping track of all of the stuff... we lift! Login with username ron_furgandy password pumpup.

This is a two-page app: the login page and this incredible page: where we can record that - while programming today - we lifted our cat 10 times. I love exercise! Everything on this page works via AJAX and JavaScript... but the JavaScript is pretty traditional. If you watched our Webpack tutorial, we've actually reset this project back to before we introduced Webpack. Yep, in the public/ directory, there are some normal CSS and JavaScript files. Nothing special.

Oh, and this is a Symfony 4 application... but that doesn't matter much. For you Symfony users out there, the only special setup I've done is to install the Asset component so that we can use the Twig asset() function:

<!DOCTYPE html>
<html lang="en">
... lines 4 - 10
{% block stylesheets %}
... lines 12 - 13
<link href="{{ asset('assets/css/main.css') }}" rel="stylesheet" />
{% endblock %}
... lines 16 - 17
... lines 19 - 108

On a fresh Symfony 4 project, run:

composer require asset

to get it.

The Magical require Statement

Ok... so what's all the fuss about with Webpack anyways? Well, the JavaScript file that runs the main page is called RepLogApp.js. Look inside: it holds two classes:

'use strict';
(function(window, $, Routing, swal) {
let HelperInstances = new WeakMap();
class RepLogApp {
... lines 8 - 192
* A "private" object
class Helper {
... lines 199 - 226
const rowTemplate = (repLog) => `
<tr data-weight="${repLog.totalWeightLifted}">
<a href="#"
<span class="fa fa-trash"></span>
window.RepLogApp = RepLogApp;
})(window, jQuery, Routing, swal);

If you haven't see the class syntax in JavaScript, go back and watch episode 2 of our JavaScript series. It's cool stuff.

Anyways, we have a class RepLogApp and then.... way down below, we have Helper:

'use strict';
(function(window, $, Routing, swal) {
... lines 4 - 6
class RepLogApp {
... lines 8 - 192
* A "private" object
class Helper {
... lines 199 - 226
... lines 228 - 245
})(window, jQuery, Routing, swal);

In PHP, we would never do this: we would organize each class into a different file. But in JavaScript, that's a pain! Because, if I move this Helper code to another file, then in my template, I need to remember to include a second script tag:

... lines 1 - 53
{% block javascripts %}
... lines 55 - 57
<script src="{{ asset('assets/js/RepLogApp.js') }}"></script>
... lines 59 - 65
{% endblock %}

This is why we can't have nice things.

But... what if we could require files in JavaScript... just like we can in PHP? Um... let's try it! Copy the Helper class, remove it, then - in the js/ directory, add a new file: RepLogHelper.js. Paste the class here - I'll remove the comment on top:

'use strict';
class Helper {
constructor(repLogs) {
this.repLogs = repLogs;
calculateTotalWeight() {
return Helper._calculateWeights(
getTotalWeightString(maxWeight = 500) {
let weight = this.calculateTotalWeight();
if (weight > maxWeight) {
weight = maxWeight + '+';
return weight + ' lbs';
static _calculateWeights(repLogs) {
let totalWeight = 0;
for (let repLog of repLogs) {
totalWeight += repLog.totalWeightLifted;
return totalWeight;
... lines 33 - 35

You see, in Node - which is server-side JavaScript, they have this idea of modules. Each file is a "module"... which doesn't mean much except that each file can export a value from itself. Then, other files, um, modules, can require that file to get that value.

In RepLogHelper.js, we really to make this Helper class available to other files. To export it, at the bottom, add module.exports = Helper:

'use strict';
class Helper {
... lines 4 - 31
module.exports = Helper;

Now, in RepLogApp, at the top, add const Helper = require('./RepLogHelper');:

'use strict';
const Helper = require('./RepLogHelper');
(function(window, $, Routing, swal) {
... lines 6 - 213
})(window, jQuery, Routing, swal);

I want to highlight two things. First, you do not need the .js at the end of the filename. You can add it... but you don't need it - it's assumed. Second, the ./ is important: this tells the require function to look relative to this file. Later, we'll find out what it means to not start with ./.

So here's the reality: if we ran this code on the server via Node... it would work! Yea! This require() thing is real! But... does it work in a browser?

Let's find out! Move over, open the debugging console and... refresh! Oh man!

require is not defined

Booo! So... the require() function is not something that works in a browser... in any browser. And, the thing is, it can't work. PHP and Node are server-side languages, so Node can instantly read this file from the filesystem. But in a browser, in order to get this RepLogHelper.js file, it would need to make an AJAX request... and of course that's far from instant.

The point is: the require() function just doesn't make sense in a browser. And this is the problem that Webpack solves. Webpack is a command that can read this file, parse through all of the require calls and create one final JavaScript file packed with all the code we need.

But, we're not going to install Webpack directly. Google for "Webpack Encore" to find its documentation on

Installing Webpack Encore

Click into the Installation page and copy the yarn add line. And, some background: Webpack is a Node executable, so you'll need to make sure it's installed. And second... Node has two package managers: yarn and npm. You can use either - I'll use Yarn. So make sure you have that installed too.

Then, find your terminal, open a fresh new tab, lift your cat, and then run:

yarn add @symfony/webpack-encore --dev


Encore version 0.21.0 contains a few cool changes. Don't worry, we'll tell you in this tutorial where anything is now different.

If you're a Symfony user, there is also a composer line you can use. Actually, all it really does is install a Flex recipe that creates a few files for you to get you started faster. We'll do everything manually so that we can see how it works.

Move back and... it's done! If you're new to Yarn, this did two things. First, it created a package.json file:

6 lines package.json
"devDependencies": {
"@symfony/webpack-encore": "^0.19.0"

That's just like composer.json for Node - and also a yarn.lock file - that's like composer.lock. Second, it downloaded everything into a node_modules/ directory: that's the vendor/ directory for Node.

And just like in PHP, we do not want to commit all those vendor files. Open your .gitignore file and ignore /node_modules/*:

18 lines .gitignore
... lines 2 - 18

Brilliant! Encore is installed. Let's do some webpacking!

Leave a comment!

  • 2018-09-26 Diego Aguiar

    Hey Tom Moore

    Course's code is fixed! If you download it again you should not see that error again.


  • 2018-09-25 weaverryan

    Hey Tom Moore!

    Ah, you're right! This bit us on a few tutorials! We're on it - thanks for the head's up!


  • 2018-09-23 Tom Moore

    In case it's helpful for other users - or the SymfonyCasts team can do some updates - after downloading the code and trying to run `composer install` as per the instructions, I got the following error:
    Declaration of Symfony\Flex\ParallelDownloader::getRemoteContents($originUrl, $fileUrl, $context) should be compat
    ible with Composer\Util\RemoteFilesystem::getRemoteContents($originUrl, $fileUrl, $context, ?array &$responseHeade
    rs = NULL)
    I googled it and found a related thread and solution (, which is to run `composer update symfony/flex --no-plugins` and then `composer install`.

  • 2018-04-03 Cesar Delgado

    Thanks Victor. I only wanted to be sure because of the polyfill. I like encore every time more... ;)

  • 2018-04-02 Victor Bocharsky

    Hey Cesar,

    As you can see, babel core, loader, and preset-env packs come out of the box with Encore: , so Probably don't need to install them manually, though it makes sense to specify them explicitly. Actually syntax means "classes" too, so I think it should work. Or you can always create a .babelrc file for more configuration if needed, or configure it manually in webpack.config.js like in the docs you mentioned


  • 2018-03-31 Cesar Delgado

    Hi Guys. Quick question, after installing Encore, do I have to install a preset or a polyfill for Babel? I have understood the babel is automatically configured using Encore ( but I am not sure if I need to install something else or do any other configuration. What I need is to be able to use new ES6 like you show in your preview tutorial, not only syntax but classes too.

  • 2018-03-13 Kevin Imbrechts

    Thanks Diego Aguiar !

  • 2018-03-13 Diego Aguiar

    Hey Kevin Imbrechts

    Excellent question, and actually, you are right about the best practice. I believe Ryan did it that way for simplicity, and because before using Encore on this project its *JS* files had to be publicly accessible.

    Maybe before finishing this tutorial we will see Ryan moving them into "roo/assets" :)


  • 2018-03-12 Kevin Imbrechts

    Why did you have organize assets in public/assets directory?
    When you install asset, an assets/ directory is created and, in the best practices of SF4, it's recommanded to store your assets in the assets/ directory at the root of your project.


  • 2018-03-06 Diego Aguiar

    Hey David Patterson

    I just checked the project and it looks fine. I think you got confused because this tutorial is a continuation of our previous tutorial (Webpack for Module Loading Awesomeness), the one different thing is that this project is updated to work on Symfony4
    If I am wrong, please let me know


  • 2018-03-06 David Patterson

    Hmmm. Looks like the course code download isn't correct.
    The file is named, but the contents appear to be for the Javascript for PHP Geeks Tutorial.
    The unzipped directory contains directories named finish/ and start/, and a The README does refer to Webpack Encore, but the start/ and finish/ directories appear to be for the Javascript tutorial.