Make custom webpack config more flexible

By adopting a scheme borrowed from next.js, where a function is defined
that can alter the default config.

https://github.com/zeit/next.js#customizing-webpack-config

src/DEFAULTS.js

@@ -12,3 +12,8 @@ export const hooks = {
     console.log(result);
   }
 }
+export function customizeWebpackConfig(config) {
+  // provide a default no-op for this config option so that we can assume it's
+  // always there.
+  return config;
+}

src/createWebpackBundle.js

@@ -6,29 +6,25 @@ import webpack from 'webpack';
 
 const OUTFILE = 'enduire.js';
 
-export default function createWebpackBundle(entry, { webpackLoaders }) {
+export default function createWebpackBundle(entry, { customizeWebpackConfig }) {
+  const config = customizeWebpackConfig({
+    entry,
+    resolve: {
+      extensions: ['*', '.js', '.jsx', '.json'],
+    },
+    output: {
+      filename: OUTFILE,
+      path: os.tmpdir(),
+    },
+  });
+
   return new Promise((resolve, reject) => {
-    webpack(
-      {
-        entry,
-        resolve: {
-          extensions: ['*', '.js', '.jsx', '.json'],
-        },
-        output: {
-          filename: OUTFILE,
-          path: os.tmpdir(),
-        },
-        module: {
-          rules: webpackLoaders,
-        },
-      },
-      (err, stats) => {
-        if (err) {
-          reject(err);
-          return;
-        }
-        resolve(path.join(os.tmpdir(), OUTFILE));
-      },
-    );
+    webpack(config, (err, stats) => {
+      if (err) {
+        reject(err);
+        return;
+      }
+      resolve(path.join(os.tmpdir(), OUTFILE));
+    });
   });
 }

src/index.js

@@ -1,3 +1,5 @@
+import 'babel-polyfill';
+
 import RemoteBrowserTarget from './RemoteBrowserTarget';
 import fetchReport from './fetchReport';
 import uploadReport from './uploadReport';

src/reactDOMRunner.js

@@ -8,7 +8,7 @@ export default async function reactDOMRunner({
   apiKey,
   apiSecret,
   setupScript,
-  webpackLoaders,
+  customizeWebpackConfig,
   stylesheets,
   include,
   targets,
@@ -18,7 +18,7 @@ export default async function reactDOMRunner({
   const entryFile = await createDynamicEntryPoint({ setupScript, include });
 
   console.log('Producing bundle...');
-  const bundleFile = await createWebpackBundle(entryFile, { webpackLoaders });
+  const bundleFile = await createWebpackBundle(entryFile, { customizeWebpackConfig });
 
   const cssBlocks = await Promise.all(stylesheets.map(loadCSSFile));
 

src/runForSha.js

@@ -1,10 +1,3 @@
-import constructReport from './constructReport';
-import createDynamicEntryPoint from './createDynamicEntryPoint';
-import createWebpackBundle from './createWebpackBundle';
-import fetchReport from './fetchReport';
-import loadCSSFile from './loadCSSFile';
-import loadUserConfig from './loadUserConfig';
-import processSnapsInBundle from './processSnapsInBundle';
 import uploadReport from './uploadReport';
 
 export default async function runForSha(sha, {