Use rollup to create an UMD module build

Closes #1

.gitignore

@@ -1,3 +1,4 @@
 node_modules/
 .source.*
 .nyc_output/
+dist/

package.json

@@ -4,10 +4,13 @@
   "description": "Fetch DB entries in batches to improve performance while respecting IPC size constraints",
   "license": "MIT",
   "author": "Raphael von der Grün",
-  "main": "dexie-batch.js",
+  "main": "dist/dexie-batch.js",
+  "module": "dist/dexie-batch.mjs",
   "repository": "raphinesse/dexie-batch",
   "scripts": {
+    "build": "rollup -c",
     "format": "prettier --ignore-path .gitignore --write '**/*.js'",
+    "prepublishOnly": "npm run build",
     "test": "xo && nyc ava"
   },
   "xo": {
@@ -20,11 +23,17 @@
     "singleQuote": true,
     "trailingComma": "es5"
   },
+  "files": [
+    "dist"
+  ],
   "devDependencies": {
     "ava": "^0.25.0",
     "dexie": "^2.0.1",
     "fake-indexeddb": "^2.0.3",
     "nyc": "^11.6.0",
+    "rollup": "^0.57.1",
+    "rollup-plugin-commonjs": "^9.1.0",
+    "rollup-plugin-node-resolve": "^3.3.0",
     "xo": "^0.20.3"
   },
   "peerDependencies": {

rollup.config.js

@@ -0,0 +1,36 @@
+import resolve from 'rollup-plugin-node-resolve'
+import commonjs from 'rollup-plugin-commonjs'
+
+const pkg = require('./package')
+
+const banner = (_ => {
+  const id = `${pkg.name} v${pkg.version}`
+  const homepage = 'github.com/' + pkg.repository
+  const license = `${pkg.license} License`
+  return `/*! ${id} | ${homepage} | ${license} */`
+})()
+
+function outputConfig(config) {
+  const defaultConfig = {
+    sourcemap: true,
+    banner,
+  }
+  return Object.assign(defaultConfig, config)
+}
+
+export default {
+  input: 'dexie-batch.js',
+  output: [
+    // Browser-friendly UMD build
+    outputConfig({
+      file: pkg.main,
+      name: 'DexieBatch',
+      format: 'umd',
+      globals: { dexie: 'Dexie' },
+    }),
+    // ECMAScript module build
+    outputConfig({ file: pkg.module, format: 'es' }),
+  ],
+  external: ['dexie'],
+  plugins: [resolve(), commonjs()],
+}