Can I use webpack to generate CSS and JS separatel

Question

I have:

1. JS files that I want to bundle.
2. LESS files that I want to compile down to CSS (resolving @imports into a single bundle).

I was hoping to specify these as two separate inputs and have two separate outputs (likely via extract-text-webpack-plugin). Webpack has all the proper plugins/loaders to do compilation, but it doesn't seem to like the separation.

I've seen examples of people requiring their LESS files directly from JS, such as require('./app.less');, for no other reason than to tell webpack to include those files into the bundle. This allows you to only have a single entry point, but it seems really wrong to me -- why would I require LESS in my JS when it has nothing to do with my JS code?

I tried using multiple entry points, handing both the entry JS and main LESS file in, but when using multiple entry points, webpack generates a bundle that doesn't execute the JS on load -- it bundles it all, but doesn't know what should be executed on startup.

Am I just using webpack wrong? Should I run separate instances of webpack for these separate modules? Should I even be using webpack for non-JS assets if I'm not going to mix them into my JS?

Answer 1

You can also put your Less require statements in your entry JS file also:

in body.js

// CSS
require('css/_variable.scss')
require('css/_npm.scss')
require('css/_library.scss')
require('css/_lib.scss')

Then in webpack

  entry: {
    body: [
      Path.join(__dirname, '/source/assets/javascripts/_body.js')
    ]
  },

const extractSass = new ExtractTextPlugin({
  filename: 'assets/stylesheets/all.bundle.css',
  disable: process.env.NODE_ENV === 'development',
  allChunks: true
})

Answer 2

A separate CSS bundle can be generated without using require('main/less) in any of your JS, but as Brendan pointed out in the first part of his answer Webpack isn't designed for a global CSS bundle to go alongside modular JS, however there are a couple of options.

The first is to add an extra entry point for main.less, then use the Extract Text plugin to create the CSS bundle:

var webpack = require('webpack'),
    ExtractTextPlugin = require("extract-text-webpack-plugin");

module.exports = {
    entry: {
        home: [
            'js/common',
            'js/homepage'
        ],
        style: [
            'styles/main.less'
        ]
    },
    output: {
        path: 'dist',
        filename: "[name].min.js"
    },
    resolve: {
        extensions: ["", ".js"]
    },
    module: {
        loaders: [{
            test: /\.less$/,
            loader: ExtractTextPlugin.extract("style", "css", "less")
        }]
    },
    plugins: [
        new ExtractTextPlugin("[name].min.css", {
            allChunks: true
        })
    ]
};

The problem with this method is you also generate an unwanted JS file as well as the bundle, in this example: style.js which is just an empty Webpack module.

Another option is to add the main less file to an existing Webpack entry point:

var webpack = require('webpack'),
    ExtractTextPlugin = require("extract-text-webpack-plugin");

module.exports = {
    entry: {
        home: [
            'js/common',
            'js/homepage',
            'styles/main.less'
        ],
    },
    output: {
        path: 'dist',
        filename: "[name].min.js"
    },
    resolve: {
        extensions: ["", ".js"]
    },
    module: {
        loaders: [{
            test: /\.less$/,
            loader: ExtractTextPlugin.extract("style", "css", "less")
        }]
    },
    plugins: [
        new ExtractTextPlugin("[name].min.css", {
            allChunks: true
        })
    ]
};

This is ideal if you have only 1 entry point, but if you have more, then your Webpack config will look a bit odd as you'll have to arbitrarily choose which entry point to add the main less file to.

Answer 3

Yes, this is possible but like others said you will need additional packages to do so (see devDependencies under package.json). here is the sample code that I used to compile my bootstrap SCSS --> CSS and Bootstrap JS --> JS.

webpack.config.js:

module.exports = {
    mode: process.env.NODE_ENV === 'production' ? 'production' : 'development',
    entry: ['./src/app.js', './src/scss/app.scss'],
    output: {
    path: path.resolve(__dirname, 'lib/modules/theme/public'),
    filename: 'js/bootstrap.js'
    },
    module: {
        rules: [
            {
                test: /\.scss$/,
                use: [
                    {
                        loader: 'file-loader',
                        options: {
                            name: 'css/bootstrap.css',
                        }
                    },
                    {
                        loader: 'extract-loader'
                    },
                    {
                        loader: 'css-loader?-url'
                    },
                    {
                        loader: 'postcss-loader'
                    },
                    {
                        loader: 'sass-loader'
                    }
                ]
            }
        ]
    }
};

additional postcss.config.js file:

module.exports = {
    plugins: {
        'autoprefixer': {}
    }
}

package.json:

{
  "main": "app.js",
  "scripts": {
    "build": "webpack",
    "start": "node app.js"
  },
  "author": "P'unk Avenue",
  "license": "MIT",
  "dependencies": {
    "bootstrap": "^4.1.3",
  },
  "devDependencies": {
    "autoprefixer": "^9.3.1",
    "css-loader": "^1.0.1",
    "exports-loader": "^0.7.0",
    "extract-loader": "^3.1.0",
    "file-loader": "^2.0.0",
    "node-sass": "^4.10.0",
    "popper.js": "^1.14.6",
    "postcss-cli": "^6.0.1",
    "postcss-loader": "^3.0.0",
    "sass-loader": "^7.1.0",
    "style-loader": "^0.23.1",
    "webpack": "^4.26.1",
    "webpack-cli": "^3.1.2"
  }
}

See the tutorial here: https://florianbrinkmann.com/en/4240/sass-webpack

Answer 4

Should I even be using webpack for non-JS assets if I'm not going to mix them into my JS?

Maybe not. Webpack is definitely js-centric, with the implicit assumption that what you're building is a js application. Its implementation of require() allows you to treat everything as a module (including Sass/LESS partials, JSON, pretty much anything), and automatically does your dependency management for you (everything that you require is bundled, and nothing else).

why would I require LESS in my JS when it has nothing to do with my JS code?

People do this because they're defining a piece of their application (e.g. a React component, a Backbone View) with js. That piece of the application has CSS that goes with it. Depending on some external CSS resource that's built separately and not directly referenced from the js module is fragile, harder to work with, and can lead to styles getting out of date, etc. Webpack encourages you to keep everything modular, so you have a CSS (Sass, whatever) partial that goes with that js component, and the js component require()s it to make the dependency clear (to you and to the build tool, which never builds styles you don't need).

I don't know if you could use webpack to bundle CSS on its own (when the CSS files aren't referenced from any js). I'm sure you could wire something up with plugins, etc., but not sure it's possible out of the box. If you do reference the CSS files from your js, you can easily bundle the CSS into a separate file with the Extract Text plugin, as you say.

Answer 5

To further clarify bdmason's former answer - it seems the desirable configuration would be to create a JS and CSS bundle for each page, like so:

 entry: {
        Home: ["./path/to/home.js", "./path/to/home.less"],
        About: ["./path/to/about.js", "./path/to/about.less"]
    }

And then use the [name] switch:

output: {
        path: "path/to/generated/bundles",
        filename: "[name].js"
    },
plugins: new ExtractTextPlugin("[name].css")

Full configuration - with some additions not connected to the question (we're actually using SASS instead of LESS):

var ExtractTextPlugin = require("extract-text-webpack-plugin");
var debug = process.env.NODE_ENV !== "production";
var webpack = require('webpack');
require('babel-polyfill');

module.exports = [{
    devtool: debug ? "inline-sourcemap" : null,
    entry: {
        Home: ['babel-polyfill', "./home.js","path/to/HomeRootStyle.scss"],
        SearchResults: ['babel-polyfill', "./searchResults.js","path/to/SearchResultsRootStyle.scss"]
    },
    module: {
        loaders: [
            {
                test: /\.jsx?$/,
                exclude: /(node_modules|bower_components)/,
                loader: 'babel-loader',
                query: {
                    presets: ['react', 'es2015'],
                    plugins: ['react-html-attrs', 'transform-class-properties', 'transform-decorators-legacy']
                }
            },
            {
                test: /\.scss$/,
                loader: ExtractTextPlugin.extract("style-loader","css-raw-loader!sass-loader")
            }
        ]
    },
    output: {
        path: "./res/generated",
        filename: "[name].js"
    },
    plugins: debug ? [new ExtractTextPlugin("[name].css")] : [
        new ExtractTextPlugin("[name].css"),
        new webpack.DefinePlugin({
            'process.env':{
                'NODE_ENV': JSON.stringify('production')
            }
        }),
        new webpack.optimize.UglifyJsPlugin({
            compress:{
                warnings: true
            }
        })
    ]
}
];