Custom Panel / js_url

Looking at the documentation at thel ink below, it’s not clear to me what js_url is supposed to point to. Whether I point it at a specific js file (e.g. /my-panel/index.js) or an implicit path (e.g., a full URL like: http://localhost:8080/my-panel), I get “Uncaught SyntaxError: Unexpected token ‘<’”.

What is it expecting?

Thanks in advance.