Using webpack with an existing PHP and JS project

First, to answer your smaller questions:

No, you're not supposed to run your PHP application through a webpack dev server. Explained in the Live Reloading section below.
No, you won't have to rewrite your assets. Probably. See the CSS and Edge Cases sections below.

Disclaimer: I'll only take on a small fraction of your question. Its scope is just way too broad to be packed into just one StackOverflow answer.

I will only get in touch with

setting up a development and a production environment for webpack
bundling your first JavaScript

which should give you a foundation to build on.

I'll also mention some things you may want to add and link according resources to read through.

So, let's go.

Requirements

I assume you have Node.js and npm installed on your machine and roughly know how to use them.

I also assume you have webpack and webpack-cli installed as (dev) dependencies of your project (not just globally):

npm install --save-dev webpack webpack-cli

Update: Earlier versions of this answer did not require installing webpack-cli. As of version 4 (February 2018), webpack's CLI resides in its own package, hence the additional required package.

Set up development and a production workflow

You usually want to do stuff differently in development than in production (minifying in production, live-reloading in development, ...)

To achieve that, we'll want to split up our configuration files.

Prepare the directory structure

Let's agree to ignore the webpack config from your question. We'll start all over, we'd have to change almost everything anyway.

First, create a build folder inside your project root. Build-related stuff will go there, since we don't want to pollute your project's root folder with config files. (You're free to name this folder differently, but keep track of that during this tutorial.)

Create a config.base.js, a config.production.js and a config.development.js file inside that folder.

Great, we have config files for two build chains now. The configurations are still empty though, so let's now fill them with some basic logic.

Install `webpack-merge`

But first, we'll need to install webpack-merge.

npm install --save-dev webpack-merge

This package allows us to deeply merge multiple webpack configurations. We want to use it to create webpack configurations depending on our current environment.

Adjust your configuration

Now adjust your build/config.base.js:

module.exports = {
  // We'll place webpack configuration for all environments here
}

The file does obviously just export an empty object right now, but we'll need that for the following steps.

Put this code in your build/config.production.js:

const { merge } = require('webpack-merge')

module.exports = merge(require('./config.base.js'), {
  mode: 'production'
  
  // We'll place webpack configuration for production environment here
})

And almost the same code goes into your build/config.development.js:

const { merge } = require('webpack-merge')

module.exports = merge(require('./config.base.js'), {
  mode: 'development',
  watch: true
  
  // All webpack configuration for development environment will go here
})

I guess it's pretty intuitive what this does:

Using webpack with the config.development.js configuration will fetch the common configuration and merge its own config declaration in.

Update: The mode option in the above config files was added in webpack 4 (released February 2018). It sets a bunch of sensible defaults for development and production bundles.

Now running the process would look like this from the command line:

npx webpack --config build/config.development.js

# If the above doesn't work, you probably have an older version of npm (< 5.1) installed
# While npx is a really great tool, you can of course still call the path of the webpack executable manually:

node_modules/.bin/webpack --config build/config.development.js

...and vice versa for the production environment.

That command is rather clunky to use, but no worries, we'll address that later.

Make some helper files

There are information we'll be wanting to centralize to make them easily exchangeable. File paths are such a thing. So let's extract them.

Create a paths.js in your build folder and have it export some paths we'll want to use later:

const path = require('path')

// I'm really just guessing your project's folder structure from reading your question,
// you might want to adjust this whole section
module.exports = {
  // The base path of your source files, especially of your index.js
  SRC: path.resolve(__dirname, '..', 'public'),

  // The path to put the generated bundle(s)
  DIST: path.resolve(__dirname, '..', 'public', 'dist'),

  /*
  This is your public path.
  If you're running your app at http://example.com and I got your DIST folder right,
  it'll simply be "/dist".
  But if you're running it locally at http://localhost/my/app, it will be "/my/app/dist".
  
  That means you should probably *not* hardcode that path here but write it to a
  machine-related config file. (If you don't already have something like that,
  google for "dotenv" or something similar.)
  */
  ASSETS: '/dist'
}

Create aliases

As mentioned above, we could technically run our build chain in development mode like this:

npx webpack --config build/config.development.js

That's an uncomfortably verbose command though, so let's change that.

It's way more convenient to run your build process via npm scripts. Add one script per environment to your package.json like this:

{
  "scripts": {
    "dev": "webpack --config build/config.development.js",
    "prod": "webpack --config build/config.production.js"
  }
}

Now you can run your build chains with npm run dev resp. npm run prod – which is much easier to memorize and faster to type.

...as soon as there'es anything to build, of course.

Bundle JavaScript

Okay, that was actually a fair amount of work without achieving too much so far.

So let's start with something more exciting: We'll define a JavaScript entry point.

Define an entry point

Put the following code into your build/config.base.js (replacing the existing code entirely):

const path = require('path')
const { SRC, DIST, ASSETS } = require('./paths')

module.exports = {
  entry: {
    scripts: path.resolve(SRC, 'js', 'index.js')
  },
  output: {
    // Put all the bundled stuff in your dist folder
    path: DIST,

    // Our single entry point from above will be named "scripts.js"
    filename: '[name].js',

    // The output path as seen from the domain we're visiting in the browser
    publicPath: ASSETS
  }
}

Create the JavaScript file

The above configuration expects an index.js to live in your SRC/js folder (as defined in the build/paths.js).

Let's create that file with the following content:

import './jquery.min.js'
import './jquery.migrate.js'
import './jquery.bxslider.min.js'
import './jquery.appear.js'
import './jquery.countTo.js'
import './bootstrap.js'

As you can see, the index.js just imports all of the files you want to use.

If you now run

npm run prod

from your terminal, a scripts.js file will be created in your DIST folder. You can include that into your markup with a plain ol' <script> tag.

Congratulations, you've got a working webpack setup!

Dive deeper

This mini-tutorial really just scraped the surface of what you can do with webpack. It gives you a pretty solid foundation for your configuration which you now can fill with whatever you need. And that will actually be quite a lot of stuff.

I'll list a few more things you may want to enhance, with some links to read through.

webpack Concepts

If you want to use webpack, it can be hard to do so if you don't know about its underlying concepts. Juho Vepsäläinen created a great guide on getting started with webpack which helped me a whole lot. He's also a webpack core contributor so you can be sure he knows what he's talking about.

Especially loaders are a concept you'll really need to know.

Many of the hints on this list are also explained there.

Read more: SurviveJS – webpack tutorial

Code Splitting

It does what the name's saying: You might not want to pack all your JavaScript into one bulky output file.

It's a job webpack does for you to split off parts of your bundle which you only need on certain pages of your application.

Also, depending on how frequently you're working on your project's JavaScript, it might be a good idea to split off third party code from your bundle for caching purposes.

Read more: webpack Documentation – Code Splitting

Caching

You may want to enhance your site's caching behaviour by adding a hash to your bundled file names which depends on their content. This will create (for example) a script.31aa1d3cad014475a618.js instead of a scripts.js.

That file can then be cached indefinitely because as soon as its contents change, the file name will change as well.

Your PHP code might then use the webpack-manifest-plugin to gain access to the generated file names.

Immutable Caching on how to cache your bundles forever
webpack Documentation – chunkhash on how to enrich your bundle file names with hashes
webpack-manifest-plugin on how to generate a manifest.json containing the file names of your current bundle

Transpiling

In case you want to use modern ES2015 code in your site's JavaScript (and are targeting non-evergreen browsers), you'll want to transpile them down to regular ES5. (If the term "ES2015" does not make any sense to you, you're most likely not using it and can ignore this paragraph.)

Read more: babel-loader – A loader that runs Babel on your scripts

CSS

There are webpack loaders for CSS. And Sass. And PostCSS. Whatever you need.

And since you're probably not planning to include your CSS via <script> tags, get to know the Extract Text Plugin to generate actual .css files.

Update: The Extract Text Plugin is very established. However, it's actually a kind of hack: It generates .css files even though webpack only knows JavaScript as its target language.

However, this is no longer true as of webpack 4. There's now a system to define arbitrary module types, including CSS.

Long story short: Expect native CSS support in webpack to replace Extract Text Plugin some time soon.

Hint: Paths

I'll mention this because this was a real pain point for me until I realized how webpack works here:

Be aware that webpack will recognize your url(...) statements and try to resolve them relative to your source files.

This means, your source file public/css/main.css:

body {
  background: url('../img/bg.jpg');
}

if your output path is public/dist/css/bundle.css, will be transformed to:

body {
  background: url('../../img/bg.jpg');
}

style-loader and css-loader – you'll hands down need those.
extract-text-webpack-plugin

Minifying

Update: Since webpack 4 was released in February 2018, this section is rather obsolete. Setting the new mode option to "production" now automatically applies JavaScript minification.

There is a Terser plugin for webpack to minify your JavaScript. Minifying CSS is a feature already builtin to the css-loader plugin mentioned above.

Image Optimization

webpack is a bundler, not a task runner. Thus, image optimization is not a genuine webpack task. You'd probably be better off using an actual task runner or just defining some npm scripts for this.

This does not mean webpack is not capable of doing this. There are plugins for pretty much everything.

imagemin can minify images pretty nicely on its own.
imagemin-webpack-plugin will integrate that process into your webpack build chain.

Live Reloading

Your problems with live reloading have a pretty simple cause: a webpack dev server is just a simple Node.js server serving only static files.

For you're case, webpack-dev-server probably is the wrong tool at all. Try webpack-livereload-plugin instead for a live reloader that you can just include via <script> tag.

Source Maps

Update: As of webpack 4 (released in February 2018), source maps are automatically generated when the new mode option is set to "development".

By all means, use source maps. They'll make your work with bundles so much easier you'll want to cry.

Read more: webpack Documentation – Source Maps

Edge Cases

Usually, all your existing scripts you'll process with webpack should be running just fine.

The only exception that comes to my mind right now would be regarding global entities.

Look at the following code:

function myFunc () {
  console.log('I exist!')
}

This code in a plain JavaScript file would make myFunc available everywhere in your JS code. But since webpack bundle code is wrapped inside callback functions (and thus leaving the global scope), there won't be any access to that function anymore.

Third party libraries should not be a problem there, they usually assign their globals to the window object directly, but if you've already written JS code in your project, you should be aware of that.

Automate!

You'll want to automate as much of your workflow as possible.

Consider running npm run prod via a git hook before pushing / after pulling.

Hope this helps.

Using webpack with an existing PHP and JS project

Requirements

Set up development and a production workflow

Prepare the directory structure

Install `webpack-merge`

Adjust your configuration

Make some helper files

Create aliases

Bundle JavaScript

Define an entry point

Create the JavaScript file

Dive deeper

webpack Concepts

Code Splitting

Caching

Transpiling

CSS

Hint: Paths

Minifying

Image Optimization

Live Reloading

Source Maps

Edge Cases

Automate!

Tags:

Css

Php

Jquery

Node.Js

Webpack

Related

Recent Posts

Using webpack with an existing PHP and JS project

Requirements

Set up development and a production workflow

Prepare the directory structure

Install webpack-merge

Adjust your configuration

Make some helper files

Create aliases

Bundle JavaScript

Define an entry point

Create the JavaScript file

Dive deeper

webpack Concepts

Code Splitting

Caching

Transpiling

CSS

Hint: Paths

Minifying

Image Optimization

Live Reloading

Source Maps

Edge Cases

Automate!

Tags:

Css

Php

Jquery

Node.Js

Webpack

Related

Install `webpack-merge`