This post was written by Dan Barrett

By Dan Barrett

3 September 2015


webpack Article Image

We’re working on a little side project here at Humaan, and I thought it would be the perfect opportunity to try out some new-ish frameworks and build tools. For a while now, React and webpack have been all the rage, and I wanted to learn more about them. I’ve previously dabbled in React, but it was a while ago and many things have changed since then.

This article assumes you have some knowledge of JavaScript, the command line, and have Node.js installed on your system. If you have Node.js installed but haven’t used it for a while, I highly recommend updating it to the latest version.

New beginnings

With ECMAScript 6 (aka ES6 or ECMAScript 2015, hereto referred to as ES6 in this article) becoming a thing, I thought I’d also give Babel a try too. For a few months now I’ve wanted to ditch jQuery from my stack, and start writing native JavaScript. The reason for this is that ES6 has a number of new features that means it’s easier to write vanilla JavaScript, and not have to include a ~30 KB jQuery file for each site. jQuery had been a necessity for many years, especially for normalising interaction between different browsers, but as many browsers vendors are (for the most part), following the proper conventions, there’s less need for jQuery nowadays.

If you’re not familiar with webpack, it’s a similar build tool to Grunt or Gulp, but it’s also a module loader like RequireJS. While you can technically use webpack with Grunt/Gulp/etc, I’ve found I haven’t had any need to. webpack can do everything Grunt or Gulp does, and more! webpack is designed with large sites in mind so the idea is to write your JavaScript as a modularised code base so you can re-use and share code, with the goal of making it easier to maintain projects over time.

A brief summary of the stuff we’re going to use

  • webpack: build tool that uses plugins and loaders to manipulate your code
  • React: a JavaScript library that is very powerful and allows you to build large applications with data that changes over time
  • ES6: new standard for the JavaScript language (think CSS3 or HTML5)
  • Babel: transpiles modern ES6 JavaScript to older ES5 syntax for older browsers to understand
  • Sass: Amazingly powerful CSS extension language that we’re already using on all our sites

A significant part of the development stack was set up by following a great article by Jonathan Petitcolas How-to setup Webpack on an ES6 React Application with SASS? There were a few gotchas in the article, and I also wanted to write my React classes in ES6, so while Jonathan’s article was great to get set up with, it left me with a thirst of wanting to find more about ES6 and React.

In this article we’ll set up webpack to handle our CSS, images, and JavaScript. I’ll touch a little bit on React, and we’ll make a basic React app that’ll say “Hello, <name>!” and will update automatically using the very cool hot module loader. Our React app will also be written in ES6 syntax which will be transpiled to ES5 syntax by Babel.

Getting the basics set up

To get started, create a new folder on your computer, and create a package.json file then chuck the following into it:

Next, open up your command-line application of choice, and change your present working directory to the folder you created earlier. We’ve created our list of packages required, so now we need to install them by entering the following command: npm install. Give it a few minutes while all the packages are downloaded and installed to your local filesystem. Once that’s done, create a HTML file called index.html and enter the following:

As you can see, there’s absolutely nothing to the HTML page, except for the script tag referencing a currently non-existent JavaScript file.

Would the real webpack config file please stand up

Now, let’s create our webpack configuration file!  In the same folder, create a JavaScript file called webpack.config.js and enter the following:

As there’s a heap of stuff going on in this configuration file, let’s go through it line by line.

entry: getEntrySources(['./src/js/entry.js'])

This line tells the built JavaScript file all the possible entry points into the website, and which files should be loaded accordingly. If you’re going to split your JavaScript files out and only load them on certain pages, this is more important, otherwise loading all JavaScript into one bigger file will be fine.

output: {
    publicPath: 'http://localhost:8080/',
    filename: 'build/bundle.js'

The output option tells webpack what the name of the compiled JavaScript should be called (and where it should be saved), and you’ll notice it’s the same path as I specified in the HTML.  Public path isn’t necessary if you’re loading the file via the filesystem (a la file://), but if you’re serving the site through a web server, chances are this’ll be necessary (in the case of this demo, it’s necessary).

devtool: 'eval'

The devtool option determines how the sourcemap should be generated.  Depending on which tool you use to generate sourcemaps, this value can be different, but for us it’s just eval.

Next up is the module option, but as there’s two parts to it, preLoaders and loaders, I’ll do them separately.  preLoaders are used on code before it’s transformed, for example, for code hinting tools, or sourcemap tools.  loaders are used for modifying the code, and then you can even have postLoaders to handle things like tests over the generated code.  For further information regarding loaders and their order, I recommend checking out the loader documentation page.

preLoaders: [
        test: /\.jsx?$/,
        exclude: /(node_modules|bower_components)/,
        loader: 'source-map'

Using the preLoaders option, we can tell webpack which loaders we want applied to specified files.  In our case, I want to generate sourcemaps on the JavaScript files, so we tell webpack that.  The test option determines which file(s) to be used, and can be written a number of different ways – as you can see, I’m using RegExp to find all file names ending in .js or .jsx.  I’m also excluding the node_modules and bower_components folders as they can be full of hundreds if not thousands of matching files, and I don’t want to include them unless I manually import/require them.  Finally, I tell webpack which loader I want to use with the matching files, which is the source-map-loader.

Now, on to our loaders:

loaders: [
        test: /\.scss$/,
        include: /src/,
        loaders: [
            'autoprefixer?browsers=last 3 versions',
        test: /\.(jpe?g|png|gif|svg)$/i,
        loaders: [
        test: /\.jsx?$/,
        exclude: /(node_modules|bower_components)/,
        loaders: [

Our first loader can look pretty confusing at first, but it’s pretty simple really: we’re looking for all .scss files nested within the folder “src”.  Next up, we have an array of loaders that tell webpack which loaders we want to use, the order of those loaders, and the configuration options to pass on to the libraries themselves.  I find that when using a number of loaders, it’s cleaner to use the loaders array, rather than a loader string delimited by exclamation marks.

When specifying loaders using an array, the loader order is from the bottom to the top, so the SCSS files will be compiled with Sass, then Autoprefixer will work its magic, it’ll then be saved as a CSS file, and finally injected into the script with a style tag.

Next, we have options for images included in the JavaScript and CSS.  First, we test for image files, then pass them to the image loader which performs optimisations, and then generates URLs for them.  You’ll notice the limit query string of 8192.  With the limit option enabled, all files under that limit will be base64 encoded and stored in our JavaScript bundle.  Any file over that size is left as is and gets linked to via a normal URL.  Very clever stuff!

Finally, our last loader is the JavaScript handler which looks for .js or .jsx files in all folders (excluding node_modules and bower_components), then manipulate them with the Babel transpiler and the React hot module loader.

Lastly, at the bottom of the webpack configuration file we have our function that handles environments and adds extra sources depending on which environment we’re in.  By default, the environment is ‘development’.

function getEntrySources(sources) {
    if (process.env.NODE_ENV !== 'production') {

    return sources;

This function enables the webpack development server (DVS) and the hot swap loader to be considered entry-points to the script. If the environment variable NODE_ENV isn’t set to production, then add these sources.

Writing React, ES6 style!

That’s our webpack configuration sorted! It’s time to actually start writing some React and getting our app to build.

We need to build up our folder structure, so jump back to your terminal prompt and enter the following:

mkdir -p src/{js,css,img}

This will give you the structure:


In src/css, create a file called master.scss and enter the following:

Nothing too special here really, just setting a generic font size and a JPEG image to be a repeating background image. The required JPEG is below:


Now, lets create the entrypoint JavaScript file for the app!  Go to src/js and create a file called entry.js and enter what you see below:

First off, we import the CSS into our entrypoint, then we import the class HelloBox from the HelloBox file, along with React. Finally, we render the page using React, and attach it to the body.

If you tried to compile that file, it wouldn’t compile. HelloBox doesn’t exist, so it’s a bust. Let’s resolve that now, create a file called HelloBox.js:

Finally, we’ll create HelloText.js:

Awesome! We’ve written all the code we need to right now.

All the pieces come together

Remember those few scripts that were in package.json? They can act as aliases so you can run common scripts easily without having to remember how to run a certain script each time you go to run it. I defined two scripts, webpack-server, which runs the built-in webpack development server, and web-server which runs a basic Socket.IO web server (so we don’t have to deal with the file:// shortcomings).

My third script is start which is simply a wrapper around the two previous server scripts. By running npm start, it boots up both the webpack-dev-server, and the http-server with the one command. By default, the webpack dev server runs on port 8080, and we tell the HTTP server to run on port 3000. If you open up your browser and load http://localhost:3000 you’ll see:

Hello, Dan!

Sweet! Open up your DevTools window to see more information about how the hot module replacement (HMR) and webpack dev server (WDS) tools are working. You’ll also notice that the image loader found that the above JPEG is less than 8192 bytes in size, so in-lined the image as a base64 encoded image.

One of my favourite parts of webpack is the ability to pass the -p flag via the command line to enable a production-ready build of the output file which will perform optimisations like minification and uglification to your code. In our config we check for a NODE_ENV value of production – to do that, simple prefix NODE_ENV=production to your command line calls, like so: NODE_ENV=production webpack -p. Check out the webpack CLI documentation for more details.


We haven’t yet seen the real power of HMR, so split your screen up so you can see both a code editor, and your browser window (preferably with the console open). Jump into HelloBox.js and change the name from Dan to Joe. Hit save and a moment later the text will change from Hello, Dan! to Hello, Joe! HMR is much more powerful than tools like LiveReload as HMR will reload just the updated component, so if you have forms that have content entered in them, that content won’t be lost (as long as it’s not a child of the updated component).


If you get stuck on one of the code examples, check out the Bitbucket repository below to download the entire example codebase.

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  • Kir Shatrov

    I’m trying to access the source code, but the access is denied:

    • Dan Barrett

      Whoops — repo defaulted to a Private one. Changed it to public, please try now :)


      • Kir Shatrov


  • andy

    hello, i’ve cloned the repo, and your example doesn’t appear to be autoprefixing when i run it? when i look at elements with dev tools they don’t have all browser prefixed ? any help on this much appreciated.

    • Dan Barrett

      Interesting! I just gave this a go myself and noticed that “last 3 versions” doesn’t generated vendor-specific code for transitions anymore. Changing it to 4 or 5 made it generate -webkit transitions. It’s possible that since posting this, “last 3 versions” no longer requires vendor prefixes for transitions.

  • Didstopia

    Any tips on getting this to play nicely with a production environment as well? Do we just need to create separate HTML indexes for development and production, and disable publicPath in webpack.config.js?

    • Dan Barrett

      In Terminal you can do:

      NODE_ENV=’production’ webpack -p

      To get webpack to build production code, and strip out some of the hot module loader files.

      As far as your other question goes, that’s correct. Strip out the publicPath, and use different script tag locations as required. As long as your code is in a git repository, you can’t really do much harm to your codebase as you can roll back pretty easily.

  • Terry Marr

    PLEASE always add a prominent datelines to all posts — things change quickly and it’s essential to know when you wrote/updated this blog right from the get go!

    • jayhollywood

      Hi Terry, all of our posts have the date noted directly under the headline.

  • Rikki Gibson

    Thanks so much for this tutorial and the example project repo. I’m new to the npm-driven style of web development and I think this is starting to make things click.

  • Jackie

    Tried to run webpack and I am getting the following error “Module not found: Error: Cannot resolve module ‘react-hot’ …”. Do I have to install something?

    • Dan Barrett

      Hi Jackie

      I assume you’ve already done “npm install” in the root of the repository? If not, it’s possible a global version of webpack is being called (and could possibly be out of date).

      I’ve just tested the demo package and it’s working with these versions:

      Node: 5.1.0
      npm: 3.3.12
      webpack: 1.12.9

      Can you confirm the versions you’re running?

  • Mark Simon

    FYI I updated package.json using npm-check-updates and I get:

    ERROR in ./src/js/entry.js
    Module build failed: ReferenceError: [BABEL] /ProjectSamples/REACT/humaanco-demo/src/js/entry.js: Unknown option: base.stage

    • Dan Barrett

      Hi Mark

      Looks like the newest version of Babel (6.x) has a new way to configure stages. Run this in your Terminal:

      npm install babel-preset-react babel-preset-es2015 babel-preset-stage-0 –save-dev

      Then change the Babel loader configuration line to this:


      Good luck!

      Edit: I’ve also updated the repository with those changes, so it’ll work out of the box for new installations

  • pkosenko

    Beware, Babel 6 seems to have broken webpack’s ability to handle React JSX compiling using babel-loader. When you update from Babel 5 to Babel 6, Babel no longer recognizes JSX syntax (parsing has been removed from Babel core?) embedded in your javascript files. This is supposed to be resolved by adding a “react” “preset” to configuration, but that does not apparently work.

    Line 70: Unexpected token <
    | return (

    • Dan Barrett

      Hi pkosenko

      That’s right, all language-specific parsing has been removed from the core, but can be added with presets via npm. I had updated the demo repository about a month ago with the new version of Babel, but have only just updated the article now. Should work fine for you now.


  • Avi Hazut

    I’m getting the following error:
    Cannot read property ‘getAttribute’ of undefined

    Please advice.

    • Dan Barrett

      Hi Avi

      Can you please paste the full stack trace to a site like Pastebin and reply with the link to it? With no indication of where the issue is occurring, it’s a bit hard to troubleshoot.


  • JacoSwarts

    Hi, thanks for the article. I’m trying out react and webpack for the first time. I’d like to make use of JSX extensions and inline styles, so I’ve modified the code a bit, but I’m getting the following error ( my public github repo is at ) :

    ERROR in ./src/js/entry.jsx

    Module parse failed: /Users/jacoswarts/Desktop/Projects/timesheets/private/plugin-v2/src/js/entry.jsx Line 2: Unexpected token

    You may need an appropriate loader to handle this file type.

    | // Import React and JS

    | import HelloBox from ‘./HelloBox’;

    | import React from ‘react’;


    @ multi main

    Full stack at

    It seems to not recognize ES2015, could you assist perhaps?

    • Dan Barrett

      Hi Jaco

      Looks like it’s because your JavaScript files have the extension .jsx. I hadn’t set up my webpack config to support .jsx files properly. I haven’t dabbled in webpack and JSX in the last few months so that I can help you with that issue I’m afraid.

      What I did notice though that renaming the JavaScript files to .js meant that webpack could successfully compile it all.

      Best of luck though! If you figure out the problem, please let me know :)

    • Joao Pescada

      @JacoSwarts:disqus you probably got around this by now, but you’ll need to explicitly tell webpack to look for that extension. By default it only looks for javascript files without extension (also valid as directory) or one of these: “.webpack.js”, “.web.js”, “.js”. Reference:

      • JacoSwarts

        Thakns @jpescada:disqus , I recently discovered as a nice way to get started with ES6, webpack and React.

  • vincylouis

    Hi Humaan, thank you so much for the tutorial and walk through, did you ever tried to use extract-text-webpack-plugin in this project?

    if yes, are you manage to get it works?

    • Dan Barrett

      Hi vincylouis

      I have used that plugin a little bit. It has its advantages in production because of a separate stylesheet, but in development it means you can’t use HMR (Hot Module Replacement) which can be pretty useful.

  • kishore

    Hi Humaan, how does webpack works in production environment ?

    • Dan Barrett

      Hi kishore

      You can do “webpack -p” on the command line to compile your assets for production. That way they’ll be minified and as small as possible. Just upload the compiled assets to your webserver and there you go :)

  • Aseem Gupta

    I am setting up my project from scratch so that I’ve more understand of what each module installed in package.json does. I noticed, you’re just having css-loader in package.json. How can it recognize scss files which you’re. Refered

    Your package.json
    loaders: [
    { test: /.scss$/, …

    Instead it should detect css not scss

    • Dan Barrett

      Hi Aseem

      We’re using a combination of the CSS and SCSS loaders. The SCSS loader compiles the SCSS into CSS, then Autoprefixer adds vendor-specific prefixes, and then the CSS loader takes care of any URLs or requires before the Style loader wraps it in a style tag.

      If you’re just loading straight CSS, you’ll likely want to have it in this order: CSS -> Autoprefixer -> Style.

      • Aseem Gupta

        Oh Ok.. How does Autoprefixer finds which one is vendor provided files?

  • Peter Gumeson

    Only way I got hot reloading to work was by changing the order in getEntrySources() using unshift so that entry.js was last:



    Dan, this was an awesome tutorial! Keep em up.
    RE: is there a way to set this plugin to only work in production?

  • Gustavo Delgado

    Just a simple question… where are the minified css/js files? why they are not present in the main app folder? it’s a convention?