Add transpilation build step

Author: lukechilds

.gitignore

@@ -1,3 +1,5 @@
+build
+
 node_modules
 npm-debug.log
 package-lock.json

babel.config.js

@@ -0,0 +1,16 @@
+const presets = [
+  [
+    "@babel/env",
+    {
+      targets: {
+        edge: "44",
+        firefox: "66",
+        chrome: "73",
+        safari: "12",
+        ie: "9"
+      }
+    },
+  ],
+];
+
+module.exports = {presets};

package.json

@@ -2,20 +2,24 @@
   "name": "assert",
   "version": "2.0.0-prerelease",
   "description": "The assert module from Node.js, for the browser.",
-  "main": "./assert.js",
+  "main": "build/assert.js",
   "license": "MIT",
   "homepage": "https://github.com/browserify/commonjs-assert",
   "repository": "browserify/commonjs-assert",
   "scripts": {
-    "test": "node test.js",
-    "test:browsers": "airtap test.js",
+    "build": "babel assert.js test.js --out-dir build && babel internal --out-dir build/internal && babel test --out-dir build/test",
+    "test": "node build/test.js",
+    "test:browsers": "airtap build/test.js",
     "test:browsers:local": "npm run test:browsers -- --local"
   },
   "keywords": [
     "assert",
     "browser"
   ],
   "devDependencies": {
+    "@babel/cli": "^7.4.4",
+    "@babel/core": "^7.4.4",
+    "@babel/preset-env": "^7.4.4",
     "airtap": "^2.0.2",
     "cross-env": "^5.2.0",
     "tape": "^4.10.1"