REPL variable declaration and reference errors

[w1jp]

• Version:
  v10.7.0

• Platform:
  Darwin jMacBook.local 17.7.0 Darwin Kernel Version 17.7.0: Fri Jul 6 19:54:51 PDT 2018; root:xnu-4570.71.3~2/RELEASE_X86_64 x86_64

• Subsystem:
  REPL

This has been happening a few releases and I am surprised no one has reported (that I could easily find) or fixed it. When declaring a variable with 'let' or 'const' and the literal contains an error, the system will not let me redeclare the variable or use it in an assignment. In the example below, I would have expected the REPL to merely ignore my declaration after giving me the error. I should then be free to redeclare it. However, it will not let me redeclare 'a' nor reference it for an assignment.

EXAMPLE:

jon@jMacBook:wrk$ node -v
v10.7.0
jon@jMacBook:wrk$ node
> let a = a
ReferenceError: a is not defined
> let a = 1
SyntaxError: Identifier 'a' has already been declared
> a = 1
ReferenceError: a is not defined
> 

[devsnek]

this isn't really a bug. see #8309

[w1jp]

Thanks for the information-- Still a bug, but obviously a duplicate. As noted in the dialog, Babbel doesn't have this issue. Looks like its part of v8 as Safari and Chrome have the same behavior but Firefox still allows me to use the declared variable:

FIREFOX:

CHROME:

SAFARI:

[bounc3-paradise-on-e]

@w1jp

No, it's not a bug. The Node.js behavior is correct, according to the ES specification.

What you see in Babel is a Babel issue. What you see in Firefox is a gecko repl extension for devtools console. If you enable warnings in Firefox, you'll see this printed after evaluating your code:

Warning: According to the standard, after the above exception,
Warning: the global bindings should be permanently uninitialized.
Warning: We have non-standard-ly initialized them to `undefined`for you.
Warning: This nicety only happens in the JS shell.