Is there a way to add <script> tag in custom widget’s html page? I tried adding it and specified a js file as source. On button click event I mentioned a call to a function from that script. When I launch Mendix app using that custom widget and click on button; I see an error saying function not found. This made me believe that what even I mentioned in <script> tag in html is either not effective or being skipped by Mendix App.
Have you tried using the JS Snippet and inject your JS there?
I had a similar issue, but I resolved it by creating a custom button ( HTML Snippet ) and ran an onclick event ( In the JS Snippet ).