Add Package Exports configuration (#139)

* Add Package Exports configuration (semver major)

* Update compressed-size.yml

.github/workflows/compressed-size.yml

@@ -8,3 +8,5 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: preactjs/compressed-size-action@v2
+        with:
+          pattern: "./dist/*.{js,mjs,cjs}"

package.json

@@ -2,20 +2,24 @@
   "name": "mitt",
   "version": "2.1.0",
   "description": "Tiny 200b functional Event Emitter / pubsub.",
-  "jsnext:main": "dist/mitt.es.js",
-  "source": "src/index.ts",
-  "module": "dist/mitt.es.js",
-  "esmodules": "dist/mitt.modern.js",
+  "module": "dist/mitt.mjs",
   "main": "dist/mitt.js",
+  "jsnext:main": "dist/mitt.mjs",
   "umd:main": "dist/mitt.umd.js",
+  "source": "src/index.ts",
   "typings": "index.d.ts",
+  "exports": {
+    "import": "./dist/mitt.mjs",
+    "require": "./dist/mitt.js",
+    "default": "./dist/mitt.mjs"
+  },
   "scripts": {
     "test": "npm-run-all --silent typecheck lint mocha test-types",
     "mocha": "mocha test",
     "test-types": "tsc test/test-types-compilation.ts --noEmit --strict",
     "lint": "eslint src test --ext ts --ext js",
     "typecheck": "tsc --noEmit",
-    "bundle": "microbundle",
+    "bundle": "microbundle -f es,cjs,umd",
     "build": "npm-run-all --silent clean -p bundle -s docs",
     "clean": "rimraf dist",
     "docs": "documentation readme src/index.ts --section API -q --parse-extension ts",