From 6a2bd5f43f6429f8273c7d7104a45ac0f585843d Mon Sep 17 00:00:00 2001
From: Mark Erikson <mark@isquaredsoftware.com>
Date: Sun, 2 Apr 2023 22:53:53 -0400
Subject: [PATCH] Output a separate "legacy ESM" artifact for Webpack 4

---
 .github/workflows/test.yaml | 2 ++
 package.json                | 2 +-
 tsup.config.ts              | 7 ++++++-
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 691ee2f46a..26609ec159 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -16,6 +16,8 @@ jobs:
             src:
               - 'src/**'
               - 'test/**'
+              - '.github/**/*.yaml'
+              - 'tsup.config.ts'
 
   build:
     needs: changes
diff --git a/package.json b/package.json
index 2e0969f025..5c563aa8c3 100644
--- a/package.json
+++ b/package.json
@@ -24,7 +24,7 @@
     "Andrew Clark <acdlite@me.com> (https://github.com/acdlite)"
   ],
   "main": "dist/cjs/redux.cjs",
-  "module": "dist/redux.mjs",
+  "module": "dist/redux.legacy-esm.js",
   "types": "dist/redux.d.ts",
   "exports": {
     "./package.json": "./package.json",
diff --git a/tsup.config.ts b/tsup.config.ts
index c159e95953..739de93ab9 100644
--- a/tsup.config.ts
+++ b/tsup.config.ts
@@ -3,6 +3,7 @@ import { defineConfig, Options } from 'tsup'
 import * as babel from '@babel/core'
 import { Plugin } from 'esbuild'
 import { getBuildExtensions } from 'esbuild-extra'
+import fs from 'fs'
 
 // Extract error strings, replace them with error codes, and write messages to a file
 const mangleErrorsTransform: Plugin = {
@@ -42,7 +43,11 @@ export default defineConfig(options => {
       format: ['esm'],
       outExtension: () => ({ js: '.mjs' }),
       dts: true,
-      clean: true
+      clean: true,
+      onSuccess() {
+        // Support Webpack 4 by pointing `"module"` to a file with a `.js` extension
+        fs.copyFileSync('dist/redux.mjs', 'dist/redux.legacy-esm.js')
+      }
     },
     // Browser-ready ESM, production + minified
     {