Initial work on using esbuild

build.ts

@@ -0,0 +1,42 @@
+const fsPromises = require('fs/promises')
+
+const esbuild = require('esbuild')
+
+const createBuild = ({ format, env, minify = false }) => {
+  return esbuild.build({
+    entryPoints: ['src/index.ts'],
+    bundle: true,
+    minify,
+    format,
+    sourcemap: 'external',
+    define: {
+      'process.env.NODE_ENV': JSON.stringify(env)
+    },
+    outfile: `dist/redux-toolkit.${format}.${env}${minify ? '.min' : ''}.js`
+  })
+}
+
+Promise.all([
+  createBuild({ format: 'esm', env: 'production', minify: true }),
+  createBuild({ format: 'esm', env: 'development', minify: false }),
+  createBuild({ format: 'cjs', env: 'production', minify: true }),
+  createBuild({ format: 'cjs', env: 'development', minify: false }),
+  createBuild({ format: 'iife', env: 'production', minify: true }),
+  createBuild({ format: 'iife', env: 'development', minify: false })
+]).then(
+  () => {
+    return fsPromises.writeFile(
+      'dist/index.js',
+      `
+'use strict'
+
+if (process.env.NODE_ENV === 'production') {
+  module.exports = require('./redux-toolkit.cjs.production.min.js')
+} else {
+  module.exports = require('./redux-toolkit.cjs.development.js')
+}  
+`
+    )
+  },
+  () => process.exit(1)
+)