Tidying Up

RelativeCI - In-depth bundle stats analysis and monitoring - Interview with Viorel Cojocaru

The current setup doesn't clean the build directory between builds. As a result, it keeps on accumulating files as the project changes. Given this can get annoying, you should clean it up in between.

Another nice touch would be to include information about the build itself to the generated bundles as a small comment at the top of each file, including version information at least.

Cleaning the build directory#

Starting from webpack 5.20, it supports cleaning out of the box by using the following configuration:

const config = {
  output: {
    clean: true,

For earlier versions, you can either use clean-webpack-plugin or solve the problem outside of webpack. You could for example trigger rm -rf ./build && webpack or rimraf ./build && webpack in an npm script to keep it cross-platform.

Setting up output.clean#

To wrap the syntax into a function, add a function as follows.


exports.clean = () => ({
  output: {
    clean: true,

Connect the configuration as follows:


const path = require("path");
const commonConfig = merge([
... ]);

After this change, the build directory should remain tidy while building and developing. You can verify this by building the project and making sure no old files remained in the output directory.

Attaching a revision to the build#

Attaching information related to the current build revision to the build files themselves can be used for debugging. webpack.BannerPlugin allows you to achieve this. It can be used in combination with git-revision-webpack-plugin to generate a small comment at the beginning of the generated files.

Setting up BannerPlugin and GitRevisionPlugin#

To get started, install the revision plugin:

npm add git-revision-webpack-plugin -D

Then define a part to wrap the idea:


const webpack = require("webpack");
const { GitRevisionPlugin } = require("git-revision-webpack-plugin");

exports.attachRevision = () => ({
  plugins: [
    new webpack.BannerPlugin({
      banner: new GitRevisionPlugin().version(),

And connect it to the main configuration:


const productionConfig = merge([

If you build the project (npm run build), you should notice the files ending with .LICENSE.txt containing comments like /*! 0b5bb05 */ or /*! v1.7.0-9-g5f82fe8 */ in the beginning.

The output can be customized further by adjusting the banner. You can also pass revision information to the application using webpack.DefinePlugin. This technique is discussed in detail in the Environment Variables chapter.

The code expects you run it within a Git repository! Otherwise, you get a fatal: Not a git repository (or any of the parent directories): .git error. If you are not using Git, you can replace the banner with other data.

Copying files#

Copying files is another ordinary operation you can handle with webpack. copy-webpack-plugin can be handy if you need to bring external data to your build without having webpack pointing at them directly.

cpy-cli is a good option if you want to copy outside of webpack in a cross-platform way. Plugins should be cross-platform by definition.


Often, you work with webpack by identifying a problem and then discovering a plugin to tackle it. It's entirely acceptable to solve these types of issues outside of webpack, but webpack can often handle them as well.

To recap:

  • You can find many small plugins that work as tasks and push webpack closer to a task runner.
  • These tasks include cleaning the build and deployment. The Deploying Applications chapter discusses the latter topic in detail.
  • It can be a good idea to add small comments to the production build to tell what version has been deployed. This way you can debug potential issues faster.
  • Secondary tasks, like these, can be performed outside of webpack. If you are using a multi-page setup as discussed in the Multiple Pages chapter, this becomes a necessity.
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