One more try

.github/workflows/prettier.yml

@@ -0,0 +1,22 @@
+name: Check JavaScript for conformance with Prettier
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  prettier:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check out repo
+      uses: actions/checkout@v2
+    - uses: actions/cache@v2
+      name: Configure npm caching
+      with:
+        path: ~/.npm
+        key: ${{ runner.os }}-npm-${{ hashFiles('**/workflows/prettier.yml') }}
+        restore-keys: |
+          ${{ runner.os }}-npm-
+    - name: Run prettier
+      run: |-
+        npm run prettier-check

package.json

@@ -1,7 +1,7 @@
 {
   "scripts": {
-    "prettier-fix": "npx prettier --write -c ui",
-    "prettier-check": "npx prettier --check -c ui"
+    "prettier-fix": "npx prettier --write \"./**/*.js\"",
+    "prettier-check": "npx prettier --check \"./**/*.js\""
   },
   "devDependencies": {
     "prettier": "^1.19.1"