The video doesn’t show the error message - was this in gmlive-server window or GameMaker output? Can you reproduce this in an empty project?
(… though in both cases I don’t have any code to output that - it’s a matter of whose bug is this)
GMLive.js is only kind of related to GMLive.gml - they share parts of the compiler and architecture, but the way they execute code is completely different - GMLive.js generates JS code that can interact with GameMaker runtime while GMLive.gml compiles code to intermediate form (read: a pile of structs and functions) and executes that from game code.