Basic Scripting Error

I've perused the forum for awhile but haven't been to solve my issue:

I have a button with an click-event to call a javascript function. A console.log works but my own function doesn't:

drive.google.com/file/d/1Ci513tN45CRin_k0btN_xZ43aXszEc8U/view

I get this error:

I have web-worker mode OFF...what am I missing?

See Using JavaScript in Construct. Construct uses JavaScript Modules, so each file has its own scope, so showMessage is not available outside its own file. The manual section covers alternatives.