Add ESLint

.eslintrc.json

@@ -0,0 +1,16 @@
+{
+    "env": {
+      "commonjs": true,
+      "es2021": true,
+      "node": true,
+      "jest": true
+    },
+    "plugins": ["github"],
+    "extends": ["eslint:recommended", "prettier", "plugin:github/internal"],
+    "parserOptions": {
+      "ecmaVersion": 12
+    },
+    "rules": {},
+    "ignorePatterns": ["/dist/**/*.js", "/src/fixtures/", "/src/blank-configurations/"]
+  }
+

.github/workflows/lint.yml

@@ -0,0 +1,35 @@
+name: Lint code
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions:
+  contents: read
+
+# This allows a subsequently queued workflow run to interrupt previous runs
+concurrency:
+  group: '${{ github.workflow }} @ ${{ github.event.pull_request.head.label || github.head_ref || github.ref }}'
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    timeout-minutes: 2
+    steps:
+      - name: Check out repo
+        uses: actions/checkout@v3
+
+      - name: Setup Node
+        uses: actions/setup-node@v3
+        with:
+          node-version-file: 16.x
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run linter
+        run: npm run lint:check