⭐ new(build): support es module building

Closes #10

Author: kazupon

template/config/entry.js

@@ -21,6 +21,12 @@ const entries = {
     format: 'cjs',
     banner
   },
+  esm: {
+    entry: 'src/index.js',
+    dest: `dist/${pack.name}.esm.js`,
+    format: 'es',
+    banner
+  },
   production: {
     entry: 'src/index.js',
     dest: `dist/${pack.name}.min.js`,
@@ -52,12 +58,11 @@ function genConfig (opts) {
     ]
   }
 
+  const replacePluginOptions = { '__VERSION__': pack.version }
   if (opts.env) {
-    config.plugins.push(replace({
-      'process.env.NODE_ENV': JSON.stringify(opts.env),
-      '__VERSION__': pack.version
-    }))
+    replacePluginOptions['process.env.NODE_ENV'] = JSON.stringify(opts.env)
   }
+  config.plugins.push(replace(replacePluginOptions))
 
   return config
 }

template/dist/README.md

@@ -1,3 +1,13 @@
-# NOTE!
+## Explanation of Build Files
 
-The `dist` folder contains the standalone build for {{ name }}, however files here are only checked-in when a release happens. If you are on the `{{ branch }}` branch, files here are **NOT** up to date. Only the `master` branch contains the built files for the latest stable version.
+- UMD: {{ name }}.js
+- CommonJS: {{ name }}.common.js
+- ES Module: {{ name }}.esm.js
+
+### Terms
+
+- **[UMD](https://github.com/umdjs/umd)**: UMD builds can be used directly in the browser via a `<script>` tag. The default file from Unpkg CDN at [https://unpkg.com/{{ name }}](https://unpkg.com/{{ name }}) is the UMD build (`{{ name }}.js`).
+
+- **[CommonJS](http://wiki.commonjs.org/wiki/Modules/1.1)**: CommonJS builds are intended for use with older bundlers like [browserify](http://browserify.org/) or [webpack 1](https://webpack.github.io). The default file for these bundlers (`pkg.main`) is the Runtime only CommonJS build (`{{ name }}.common.js`).
+
+- **[ES Module](http://exploringjs.com/es6/ch_modules.html)**: ES module builds are intended for use with modern bundlers like [webpack 2](https://webpack.js.org) or [rollup](http://rollupjs.org/). The default file for these bundlers (`pkg.module`) is the Runtime only ES Module build (`{{ name }}.esm.js`).

template/package.json

@@ -85,14 +85,15 @@
   {{#unless_eq githubAccount ""}}
   "homepage": "https://github.com/{{ githubAccount }}/{{ name }}#readme",
   {{/unless_eq}}
+  "main": "dist/{{ name }}.common.js",
+  "module": "dist/{{ name }}.esm.js",
   "unpkg": "dist/{{ name }}.js",
   "keywords": [
     "plugin",
     "vue",
     "vuejs"
   ],
   "license": "MIT",
-  "main": "dist/{{ name }}.common.js",
   "engines": {
     "node": ">= 6.0"
   },