Microbundle is used for building dist

package.json

@@ -12,14 +12,19 @@
     "dist",
     "types"
   ],
-  "main": "dist/index.js",
   "keywords": [
     "immutable",
     "frozen",
     "functional",
     "declarative"
   ],
+  "source": "lib/index.js",
+  "main": "dist/index.js",
+  "module": "dist/index.module.js",
+  "types": "types",
   "scripts": {
+    "build": "microbundle",
+    "dev": "microbundle watch",
     "dtslint": "dtslint --localTs node_modules/typescript/lib types",
     "lint": "npm run dtslint && eslint .",
     "test": "npm run test:mocha && npm run test:karma",
@@ -61,6 +66,7 @@
     "karma-mocha-reporter": "^2.2.5",
     "karma-sourcemap-loader": "^0.3.7",
     "karma-webpack": "^4.0.2",
+    "microbundle": "^0.11.0",
     "mocha": "^7.0.0",
     "prettier": "^2.0.2",
     "rimraf": "^3.0.0",
@@ -69,6 +75,5 @@
     "webpack-cli": "^3.3.11",
     "webpack-dev-server": "^3.1.11",
     "webpack-stream": "^5.2.1"
-  },
-  "types": "types"
+  }
 }