In this case, when the body was loaded, at some point in the exercise, ‘loadZip’ did not seem to be defined.
This is a type of error which could happen to anybody – newbies and professionals alike – but, which a newbie might not understand the origin of. And, for the sake of argument, I’ll just assume for the moment, that the reader is not so much a newbie, that he or she failed to supply the file ‘viewer_z.js’, or, that within this file, he or she failed to try to define the function ‘loadZip’ (both of these being my own examples).
Next, the compiler treats the entire script, as if it had never been supplied.
On one rare occasion, the same thing happened to me, because I had put ‘await’ keywords, into a function the definition of which was not preceded by the ‘async’ keyword.
If this is happening to my reader, then chances are, they are looking for a simple error like that, and not for anything more complex.