Properly support mjs and cjs

Author: junderw

package.json

@@ -10,10 +10,22 @@
     "type": "git",
     "url": "https://github.com/bitcoinjs/uint8array-tools.git"
   },
-  "main": "src/cjs/index.js",
+  "exports": {
+    "node": {
+      "module": "./src/mjs/index.js",
+      "require": "./src/cjs/index.cjs",
+      "import": "./src/mjs/index.js"
+    },
+    "browser": "./src/mjs/browser.js",
+    "default": "./src/mjs/browser.js"
+  },
   "types": "src/cjs/index.d.ts",
+  "type": "module",
   "scripts": {
-    "build": "rm -rf src/* && tsc -p tsconfig.json && tsc -p tsconfig-cjs.json",
+    "build": "npm run clean && npm run build-ts && npm run convert-cjs && rm -f ./src/cjs/browser.d.ts",
+    "build-ts": "tsc -p tsconfig.json && tsc -p tsconfig-cjs.json",
+    "clean": "rm -rf ./src/* && rm -rf ./coverage && rm -f ./package-lock.json",
+    "convert-cjs": "for f in ./src/cjs/*.js; do mv -- \"$f\" \"${f%.js}.cjs\"; done",
     "coverage": "npm run unit -- --coverage",
     "eslint": "eslint ts_src/*.ts",
     "format": "npm run eslint -- --fix",
@@ -22,14 +34,6 @@
     "test": "npm run unit",
     "unit": "jest --config=jest.json --runInBand"
   },
-  "exports": {
-    "node": {
-      "module": "./src/mjs/index.js",
-      "require": "./src/cjs/index.js"
-    },
-    "browser": "./src/mjs/browser.js",
-    "default": "./src/mjs/index.js"
-  },
   "keywords": [
     "uint8array",
     "hex",