Mostly irrelevant, but possibly interesting variable declaration/assignment bug with let

[DanielSmedegaardBuus]

• Version: v8.1.0 (Homebrewed)
• Platform: Darwin air.local 16.6.0 Darwin Kernel Version 16.6.0: Fri Apr 14 16:21:16 PDT 2017; root:xnu-3789.60.24~6/RELEASE_X86_64 x86_64 i386 MacBookAir5,2 Darwin
• Subsystem:

Obviously, this has no impact on production code, as any script execution would die after the first error, but I find it interesting that (console) node goes into this strange state where a declared variable is broken an cannot be "fixed".

This example is just to demonstrate the issue, copy/pasted from a node console:

> let a
undefined
> a = 1
1
> let b = c
ReferenceError: c is not defined
    at repl:1:9
    at ContextifyScript.Script.runInThisContext (vm.js:44:33)
    at REPLServer.defaultEval (repl.js:239:29)
    at bound (domain.js:301:14)
    at REPLServer.runBound [as eval] (domain.js:314:12)
    at REPLServer.onLine (repl.js:433:10)
    at emitOne (events.js:120:20)
    at REPLServer.emit (events.js:210:7)
    at REPLServer.Interface._onLine (readline.js:278:10)
    at REPLServer.Interface._line (readline.js:625:8)
> b = 'c'
ReferenceError: b is not defined
    at repl:1:3
    at ContextifyScript.Script.runInThisContext (vm.js:44:33)
    at REPLServer.defaultEval (repl.js:239:29)
    at bound (domain.js:301:14)
    at REPLServer.runBound [as eval] (domain.js:314:12)
    at REPLServer.onLine (repl.js:433:10)
    at emitOne (events.js:120:20)
    at REPLServer.emit (events.js:210:7)
    at REPLServer.Interface._onLine (readline.js:278:10)
    at REPLServer.Interface._line (readline.js:625:8)
> var b = c
SyntaxError: Identifier 'b' has already been declared

> b = 1
ReferenceError: b is not defined
    at repl:1:3
    at ContextifyScript.Script.runInThisContext (vm.js:44:33)
    at REPLServer.defaultEval (repl.js:239:29)
    at bound (domain.js:301:14)
    at REPLServer.runBound [as eval] (domain.js:314:12)
    at REPLServer.onLine (repl.js:433:10)
    at emitOne (events.js:120:20)
    at REPLServer.emit (events.js:210:7)
    at REPLServer.Interface._onLine (readline.js:278:10)
    at REPLServer.Interface._line (readline.js:625:8)
>

[dnalborczyk]

Interesting. Though Chrome (59) behaves the same way. If anything, it's a v8 bug.

[bnoordhuis]

See #8309 and the issues linked therein, the tl;dr is that the variable (per spec) stays in the TDZ. I'll close this as a duplicate but if anyone has ideas for a workaround, please chime in; see also the comment about the Firefox console in the linked issue.