Use loose mode for class properties transform (#366)

Author: Andarist

.babelrc

@@ -0,0 +1,36 @@
+const { NODE_ENV } = process.env
+const test = NODE_ENV === 'test'
+const loose = true
+
+module.exports = {
+  presets: [
+    [
+      '@babel/preset-env',
+      {
+        loose,
+        ...(test ? { targets: { node: '8' } } : {})
+      }
+    ],
+    '@babel/preset-react',
+    '@babel/preset-flow'
+  ],
+  plugins: [
+    '@babel/plugin-transform-flow-strip-types',
+    '@babel/plugin-syntax-dynamic-import',
+    '@babel/plugin-syntax-import-meta',
+    ['@babel/plugin-proposal-class-properties', { loose }],
+    '@babel/plugin-proposal-json-strings',
+    [
+      '@babel/plugin-proposal-decorators',
+      {
+        legacy: true
+      }
+    ],
+    '@babel/plugin-proposal-function-sent',
+    '@babel/plugin-proposal-export-namespace-from',
+    '@babel/plugin-proposal-numeric-separator',
+    '@babel/plugin-proposal-throw-expressions',
+    test && '@babel/plugin-transform-react-jsx-source',
+    test && 'istanbul'
+  ].filter(Boolean)
+}

.babelrc.js

@@ -68,38 +68,7 @@ export default {
     flow(),
     commonjs({ include: 'node_modules/**' }),
     babel({
-      exclude: 'node_modules/**',
-      babelrc: false,
-      runtimeHelpers: true,
-      presets: [
-        [
-          '@babel/preset-env',
-          {
-            loose: true,
-            modules: false
-          }
-        ],
-        '@babel/preset-react',
-        '@babel/preset-flow'
-      ],
-      plugins: [
-        ['@babel/plugin-transform-runtime', { useESModules: !cjs }],
-        '@babel/plugin-transform-flow-strip-types',
-        '@babel/plugin-syntax-dynamic-import',
-        '@babel/plugin-syntax-import-meta',
-        '@babel/plugin-proposal-class-properties',
-        '@babel/plugin-proposal-json-strings',
-        [
-          '@babel/plugin-proposal-decorators',
-          {
-            legacy: true
-          }
-        ],
-        '@babel/plugin-proposal-function-sent',
-        '@babel/plugin-proposal-export-namespace-from',
-        '@babel/plugin-proposal-numeric-separator',
-        '@babel/plugin-proposal-throw-expressions'
-      ]
+      exclude: 'node_modules/**'
     }),
     umd
       ? replace({