Answer 1

Hi Zak,
The variable ctx was declared inside a function therefore its scope is localised to it.

You are trying to use that variable again globally (outside its current scope)

This article may help you
https://www.sitepoint.com/demystifying-javascript-variable-scope-hoisting/

Answer 2

Either make ctx global in scope or create a new variable ctx (which may be confusing for the reader, I would call it something else)

If you want to make it global, at the top of the js put var ctx; that way there is little editing to do.

Answer 3

visph is correct.

Answer 4

Anyway, 'ctx' variable should be accessed only after init() was executed (in which 'ctx' is defined) ^^
I suggest to move the lines using 'ctx' to draw in canvas inside your init() function ;)