should throw error if createEventDispatch is used after instantiation

[tanhauhau]

I read the tutorial and it says

createEventDispatcher must be called when the component is first instantiated, — you can't do it later inside e.g. a setTimeout callback.

however it does not show error if i use it in a setTimeout callback.

I only see an obscure error Uncaught TypeError: Cannot read property '$$' of undefined later on when I tried to dispatch an event.

Should I make this a compile time warning? or a runtime error?

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