Adds build-web script for transpiling an ES5 distribution

Author: spong

babel.config.js

@@ -0,0 +1,16 @@
+module.exports = {
+  env: {
+    web: {
+      presets: [
+        [
+          '@babel/preset-env',
+          {
+            useBuiltIns: 'entry',
+            modules: false,
+            corejs: 3,
+          },
+        ],
+      ]
+    },
+  },
+};

package.json

@@ -4,14 +4,16 @@
   "description": "Build an element once, move it anywhere",
   "main": "dist/cjs/index.js",
   "module": "dist/esm/index.js",
+  "browser": "dist/web/index.js",
   "types": "dist/index.d.ts",
   "files": [
     "dist/**/*.{js,ts,map}",
     "src/**/*",
     "README.md"
   ],
   "scripts": {
-    "build": "rimraf dist/ && tsc -p tsconfig.cjs.json && tsc -p tsconfig.esm.json",
+    "build": "rimraf dist/ && tsc -p tsconfig.cjs.json && tsc -p tsconfig.esm.json && npm run build-web",
+    "build-web": "BABEL_ENV=web babel dist/esm --config-file=./babel.config.js --out-dir=dist/web",
     "pretest": "npm run build",
     "test": "echo \"It built ok, that'll do for now\"",
     "prepack": "npm run build",
@@ -38,6 +40,7 @@
   },
   "homepage": "https://github.com/httptoolkit/react-reverse-portal#readme",
   "devDependencies": {
+    "@babel/cli": "^7.6.4",
     "@babel/core": "^7.5.5",
     "@storybook/addon-storysource": "^5.1.11",
     "@storybook/addons": "^5.1.11",