Add ESLint to CI/CD

.github/workflows/linter.yml

@@ -14,7 +14,7 @@ jobs:
   # [2] https://robertfaldo.medium.com/commands-to-run-rubocop-and-specs-you-changed-in-your-branch-e6d2f2e4110b
   # [3] https://community.atlassian.com/t5/Bitbucket-questions/Git-diff-show-different-files-than-PR-Pull-Request/qaq-p/2331786
   rubocop:
-    name: RuboCop
+    name: RuboCop (Ruby)
     runs-on: ubuntu-latest
     steps:
       - name: 'Checkout PR branch (with test merge-commit)'
@@ -43,3 +43,31 @@ jobs:
         run: |
           echo "🚨 Running RuboCop version: $(bundle info rubocop | head -1)"
           bundle exec rubocop --format github --fail-level 'convention' --force-exclusion -- $CHANGED_FILES
+  
+  eslint:
+      name: ESLint (JS)
+      runs-on: ubuntu-latest
+      steps:
+        - name: 'Checkout PR branch'
+          uses: actions/checkout@v4
+
+        # see notes above (in rubocop job)
+        - name: Get changed files
+          run: |
+            files=$(git diff --name-only --diff-filter=ACMR -r HEAD^1...HEAD | grep -e '\.js$' -e '\.js.erb$'|| test $? = 1;)
+            printf "🎴 Changed js files: \n$files"
+            echo "CHANGED_FILES=$(echo ${files} | xargs)" >> $GITHUB_ENV
+        
+        - name: 'Setup Node.js'
+          if: env.CHANGED_FILES != ''
+          uses: actions/setup-node@v4
+          with:
+            node-version: '20' # End of Life (EOL): April 2026
+
+        - name: 'Install dependencies'
+          if: env.CHANGED_FILES != ''
+          run: yarn install
+
+        - name: 'Run ESLint'
+          if: env.CHANGED_FILES != ''
+          run: yarn run eslint --ignore-path .gitignore --max-warnings 0 -- $CHANGED_FILES