centralise babel config

.babelrc

@@ -1,10 +1,5 @@
 {
   "presets": [
-    ["es2015", { "loose": true }],
-    "react"
-  ],
-  "plugins": [
-    "transform-class-properties",
-    ["transform-react-remove-prop-types", { "mode": "wrap" }]
+    "./preset"
   ]
 }

preset.js

@@ -0,0 +1,29 @@
+module.exports = (babel, options) => {
+  const rollup = options && options.rollup;
+  const tests = options && options.tests;
+
+  const modules = rollup ? false : 'commonjs';
+  const plugins = [
+    'transform-class-properties',
+    ['transform-react-remove-prop-types', { mode: 'wrap' }],
+  ];
+
+  if (rollup) {
+    plugins.push('external-helpers');
+  }
+  if (tests) {
+    plugins.push('syntax-async-functions');
+    plugins.push(['transform-regenerator', { async: true }]);
+  }
+
+  return {
+    presets: [
+      ['es2015', {
+        loose: true,
+        modules,
+      }],
+      'react',
+    ],
+    plugins,
+  };
+};

rollup.config.js

@@ -1,19 +1,7 @@
-import fs from 'fs';
-import path from 'path';
 import babel from 'rollup-plugin-babel';
 
 const meta = require('./package.json');
 
-// build a babel config that works for the rollup babel plugin
-function getBabelConfig() {
-  const babelrc = fs.readFileSync(path.join(__dirname, '.babelrc'), 'utf8');
-  const babelConfig = JSON.parse(babelrc);
-  babelConfig.presets[0] = ['es2015', { loose: true, modules: false }];
-  babelConfig.plugins.push('external-helpers');
-  babelConfig.babelrc = false;
-  return babelConfig;
-}
-
 export default {
   input: './src/index.js',
   output: [
@@ -24,6 +12,11 @@ export default {
   external: Object.keys(meta.dependencies)
     .concat(Object.keys(meta.peerDependencies)),
   plugins: [
-    babel(getBabelConfig()),
+    babel({
+      babelrc: false,
+      presets: [
+        [require.resolve('./preset'), { rollup: true }],
+      ],
+    }),
   ],
 };

test/.babelrc

@@ -1,7 +1,5 @@
 {
-  "extends": "../.babelrc",
-  "plugins": [
-    "syntax-async-functions",
-    ["transform-regenerator", { "async": true }]
+  "presets": [
+    ["../preset", { "tests": true }]
   ]
 }