ci: format code

Uses Prettier (https://prettier.io/) to find style issues in the code.

.github/workflows/checks.yml

@@ -0,0 +1,27 @@
+name: Checks
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+
+jobs:
+  format:
+    runs-on: ubuntu-20.04
+
+    steps:
+      - name: 'Checkout code'
+        uses: actions/checkout@v2
+
+      - name: 'Set up Node.js'
+        uses: actions/setup-node@v2
+        with:
+          node-version: 16
+          cache: ${{ !env.ACT && 'npm' || '' }}
+
+      - name: 'Install dependencies'
+        run: npm ci
+
+      - name: 'Run formatter'
+        run: npm run format

.prettierignore

@@ -0,0 +1 @@
+/.husky/_/

.prettierrc

@@ -0,0 +1,7 @@
+{
+  "arrowParens": "avoid",
+  "printWidth": 120,
+  "semi": false,
+  "singleQuote": true,
+  "trailingComma": "all"
+}

package.json

@@ -8,9 +8,13 @@
   "devDependencies": {
     "@commitlint/cli": "^16.2.3",
     "@commitlint/config-conventional": "^16.2.1",
-    "husky": "^7.0.4"
+    "husky": "^7.0.4",
+    "prettier": "^2.6.2",
+    "prettier-plugin-sh": "^0.10.0"
   },
   "scripts": {
+    "format": "prettier --ignore-unknown --check '**'",
+    "format:fix": "npm run format -- --write",
     "prepare": "which husky && husky install || true"
   }
 }