add JavaScript linting to CI (!5445)

.gitlab-ci.yml

@@ -310,6 +310,15 @@ coverage:
     - coverage/index.html
     - coverage/assets/
 
+lint-javascript:
+  stage: test
+  image: "node:latest"
+  before_script:
+    - npm install
+  script:
+    - npm run eslint
+  allow_failure: true # don't break build until old linting errors have been fixed
+
 # Trigger docs build
 trigger_docs:
   stage: post-test