Webpack configuration

A really basic webpack configuration for mocha-webpack should at least contain the following:

webpack.config-test.js - example config

var nodeExternals = require('webpack-node-externals');

module.exports = {
  target: 'node', // webpack should compile node compatible code
  externals: [nodeExternals()], // in order to ignore all modules in node_modules folder
};

The most important option is the value of target, as it tells webpack to compile the code for Node.js. When you leave this empty, webpack compiles for web environment and features like code-splitting will not work.

Another important thing is to stop webpack from bundling your libraries inside your node_modules folder. This can be easily done by using the webpack-node-externals plugin. The reason for this is that webpack isn't able to compile all node_modules like server only modules. Another reason is simply performance.

Info: You can install this plugin with npm install --save-dev webpack-node-externals

Maybe you noticed that entry and output.path are completely missing in this config. mocha-webpack does this automatically for you, but it respects custom output settings. This is especially useful, when you want to write the files to disk with an additional plugin.

Sourcemaps

Sourcemap support is already applied for you via source-map-support by mocha-webpack. You just need to enable it in your webpack config via the devtool setting.

Note: For a proper debug experience in your IDE (setting breakpoints right into your code) you need to use a devtool which inlines the sourcemaps like inline-cheap-module-source-map.

So your webpack-config should look like

webpack.config-test.js

var nodeExternals = require('webpack-node-externals');

module.exports = {
  output: {
    // use absolute paths in sourcemaps (important for debugging via IDE)
    devtoolModuleFilenameTemplate: '[absolute-resource-path]',
    devtoolFallbackModuleFilenameTemplate: '[absolute-resource-path]?[hash]'
  },
  target: 'node',  // webpack should compile node compatible code
  externals: [nodeExternals()], // in order to ignore all modules in node_modules folder
  devtool: "inline-cheap-module-source-map"
};

CSS Preprocessors

When you are using CSS Preprocessors like less, sass, or post-css then you need to think about:

• if you use CSS-Modules
• or not

When you never heard about CSS-Modules you probably don't use it.

Without CSS-Modules

If you don't want to use CSS-Modules then you can replace all of your CSS loaders with null-loader:

Your webpack-config for the browser might look like the following:

module.exports = {
    module: {
        rules: [
            // ...
            { test: /\.scss$/, use: ['style-loader', 'css-loader', 'sass-loader'] },
            { test: /\.css$/, use: ['style-loader', 'css-loader'] },
            // ...
        ]
    },
};

Replacing all CSS related loaders with null-loader results in the following config:

module.exports = {
    module: {
        rules: [
            // ...
            { test: /\.scss$/, loader: 'null-loader' },
            { test: /\.css$/, loader: 'null-loader' },
            // ...
        ]
    },
};

This has the following advantages:

• you will no longer get the following error: ReferenceError: window is not defined
• you don't have to compile your css to run your tests --> much faster

With CSS-Modules

If you want to use CSS-Modules you have to make your loader definition compatible with the node environment. It's the same setup like for universal applications respectively pre-rendering of Single Page Applications.

Your webpack-config for the browser might look like the following:

module.exports = {
    module: {
        rules: [
            // ...
            { test: /\.scss$/, use: ['style-loader', 'css-loader?modules', 'sass-loader'] },
            { test: /\.css$/, use: ['style-loader', 'css-loader?modules'] },
            // ...
        ]
    },
};

To make the config compatible with the node environment you have to do two things:

• remove style-loader
• replace css-loader with css-loader/locals

Then your config looks like this and you're ready to test:

module.exports = {
    module: {
        rules: [
            // ...
            { test: /\.scss$/, use: ['css-loader/locals?modules', 'sass-loader'] },
            { test: /\.css$/, use: ['css-loader/locals?modules'] },
            // ...
        ]
    },
};