Make sure the JS code is built

Author: hansthen

.github/workflows/test_streamlit_folium.yml

@@ -29,11 +29,17 @@ jobs:
         ref: master
         path: streamlit_folium  # Checkout into a subdirectory
 
-    - name: Install streamlit_folium
+    - name: Build streamlit_folium frontend
       run: |
         cd streamlit_folium
         pip install -e .
 
+    - name: Install streamlit_folium
+      run: |
+        cd streamlit_folium/streamlit_folium/frontend/
+        npm install
+        npm run build
+
     - name: Install streamlit_folium dev dependencies
       run: |
         pip install -r streamlit_folium/tests/requirements.txt