Variable stuck in temporal deadzone

[psykzz]

• Version: v8.11.3
• Platform: Mac OSX 10.13.4
• Subsystem: unknown

If during assignment of a let you assign a syntax error, your variable will become un-useable.
For an example let a = Ahhhh.

> let a = Ahhh
ReferenceError: Ahhh is not defined
> a
ReferenceError: a is not defined
> a = 5
ReferenceError: a is not defined
> typeof a
ReferenceError: a is not defined
> let a = 10
SyntaxError: Identifier 'a' has already been declared
>

I suspect this is related to the temporal dead zone as described at developer.mozilla.org/let#Temporal_Dead_Zone.

[devsnek]

Duplicate of #13919