Enable ES2015's (un-transpiled) module imports while supporting Webpa…

…ck's tree shaking.

This is currently *not* supported by Webpack (see webpack/webpack#1979 (comment) and webpack/webpack#2933 for rationale).

We workaround this by exposing our babel config to the wild (i.e. js/nagato/babel-options.js). This way we can give full controls for both bundling (i.e. 'tree shaking' in Webpack) and module building (i.e. 'transpiling') to the library users (I hope).

We just can't enforce our users to use some huge-sized arbitrary bundle.

Users with ES2015+ (or whatever) environment shall `require()` this config file inside their 'webpack.config.js', and use it as a hash object for the `babel-loader`'s `option: ` option. This could be achieved by looking into the `module: ` option in `package.json`; which (I believe) is the default behavior for Webpack when you use the native `import Something from 'other-external-library'` syntax.

If this is not desirable, use the fully-transpiled .js file inside our distributed npm package. This could be achieved by referring to the old-school `"main"` value inside the package.json.

Disclaimer:
By using this method we abandon Webpack-specific aggresive transpilation features for our entire library. This means we can't use Webpack-specific custom `import`s (i.e. importing non-JavaScript files like images (.png, .jpg, etc.) inside our library (.js)).

Additional notes:
This issue described in the disclaimer section can be workarounded by specifying your library-specific `npm run build` action inside the `prepare` section of package.json.

.babelrc → js/nagato/babel-options.js

@@ -1,4 +1,4 @@
-{
+module.exports = {
   "presets": [
     ["env", {
       "modules": false,
@@ -12,11 +12,6 @@
     "transform-function-bind",
     "transform-runtime",
     "transform-class-properties"
-  ],
-  "env": {
-    "production": {
-      "presets": []
-    }
-  }
+  ]
 }
 

webpack.common.js

@@ -24,6 +24,7 @@ module.exports = {
             },
             {
               loader: 'babel-loader',
+              options: require('./js/nagato/babel-options'),
             },
           ],
           exclude: /node_modules/,