Webpack bundlesize compare action

An action that compares 2 webpack compilation stats files, and comments on the PR with a description of the difference

How to use it

In your application, ensure you output the stats.json, from `BundleAnalyzerPlugin'

// webpack.config.js
const {BundleAnalyzerPlugin} = require('webpack-bundle-analyzer')

// optionally you can also output compressed/gzipped stats. Requires a version >=1.1.0
const CompressionPlugin = require('compression-webpack-plugin')

module.exports = {
  plugins: [
    ...plugins,
    // not required
    new CompressionPlugin(),

    // required
    new BundleAnalyzerPlugin({
      // generate the stats.json file
      generateStatsFile: true
    })
  ]
}

Then, in your action configuration, build both the head and the branch (in any way you see fit) and pass paths to the stats.json files as inputs ot this action

# .github/workflows/bundlesize-compare.yml

on:
  # this action will error unless run in a pr context
  pull_request:
  pull_request_target:

jobs:
  # Build current and upload stats.json
  # You may replace this with your own build method. All that
  # is required is that the stats.json be an artifact
  build-head:
    name: 'Build head'
    runs-on: ubuntu-latest
    permissions:
      contents: read
    steps:
      - uses: actions/checkout@v2
        with:
          ref: ${{github.event.pull_request.head.ref}}
      - name: Install dependencies
        run: npm ci
      - name: Build
        run: npm run build
      - name: Upload stats.json
        uses: actions/upload-artifact@v3
        with:
          name: head-stats
          path: ./dist/stats.json

  # Build base for comparison and upload stats.json
  # You may replace this with your own build method. All that
  # is required is that the stats.json be an artifact
  build-base:
    name: 'Build base'
    runs-on: ubuntu-latest
    permissions:
      contents: read
    steps:
      - uses: actions/checkout@v2
        with:
          ref: ${{ github.base_ref }}
      - name: Install dependencies
        run: npm ci
      - name: Build
        run: npm run build
      - name: Upload stats.json
        uses: actions/upload-artifact@v3
        with:
          name: base-stats
          path: ./dist/stats.json

  # run the action against the stats.json files
  compare:
    name: 'Compare base & head bundle sizes'
    runs-on: ubuntu-latest
    needs: [build-base, build-head]
    permissions:
      pull-requests: write
    steps:
      - uses: actions/download-artifact@v3
      - uses: davidatbettson/[email protected]
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          current-stats-json-path: ./head-stats/stats.json
          base-stats-json-path: ./base-stats/stats.json

This action requires the write permission for the permissions.pull-requests scope.

Options

name	description	required	type
current-stats-json-path	The path to the current stats.json file	true	string
base-stats-json-path	The path to the base stats.json file	true	string
github-token	The Github token	true	string
title	An optional addition to the title, which also helps key comments, useful if running more than 1 copy of this action	false	string
username	An optional input, defining the username of the account that places the comment. Defaults to "github-actions[bot]"	false	string

Example PR Comment

github#50 (comment)