test: add a test whether build files are es5 or not

.circleci/config.yml

@@ -19,6 +19,7 @@ commands:
       - run: yarn audit --groups dependencies
       - run: yarn lint
       - run: yarn test
+      - run: yarn test:build-assets
   # visual regression testing
   run-reg-suit:
     steps:

package.json

@@ -32,6 +32,7 @@
     "@types/react-transition-group": "^4.4.0",
     "@types/styled-components": "^5.1.0",
     "babel-loader": "^8.1.0",
+    "ecma-version-validator-webpack-plugin": "^1.0.4",
     "enzyme": "^3.11.0",
     "enzyme-adapter-react-16": "^1.15.2",
     "enzyme-to-json": "^3.5.0",
@@ -41,6 +42,7 @@
     "husky": "^4.2.5",
     "jest": "^26.0.1",
     "lint-staged": "^10.2.9",
+    "memory-fs": "^0.5.0",
     "npm-run-all": "^4.1.5",
     "prettier": "^2.0.5",
     "react": "^16.13.1",
@@ -61,7 +63,8 @@
     "stylelint-processor-styled-components": "^1.10.0",
     "ts-jest": "^26.1.0",
     "ts-loader": "^7.0.5",
-    "typescript": "^3.9.5"
+    "typescript": "^3.9.5",
+    "webpack": "^4.43.0"
   },
   "peerDependencies": {
     "react": "^16.13.0",
@@ -121,6 +124,7 @@
     "storybook": "start-storybook -p 6006",
     "test": "jest",
     "test:update-snapshot": "jest --updateSnapshot",
+    "test:build-assets": "node scripts/build-test.ts",
     "test-visual": "reg-suit run"
   },
   "sideEffects": false,

scripts/build-test.ts

@@ -0,0 +1,32 @@
+const { ECMAVersionValidatorPlugin } = require('ecma-version-validator-webpack-plugin')
+const webpack = require('webpack')
+const path = require('path')
+const MemoryFS = require('memory-fs')
+
+const compiler = webpack({
+  mode: 'development',
+  entry: path.resolve('src', 'index.ts'),
+  devtool: 'nosources-source-map',
+  plugins: [new ECMAVersionValidatorPlugin()],
+  resolve: {
+    extensions: ['.ts', '.tsx', '.js'],
+  },
+  module: {
+    rules: [
+      {
+        test: /\.tsx?$/,
+        loader: 'ts-loader',
+        exclude: /node_modules/,
+      },
+    ],
+  },
+})
+compiler.outputFileSystem = new MemoryFS()
+compiler.run((err, stats) => {
+  if (err !== null) {
+    throw err
+  }
+  if (stats.compilation.errors.length > 0) {
+    throw stats.compilation.errors
+  }
+})