1086576 - ES6-compatible let disallows variable redeclaration

Status: RESOLVED WONTFIX

(Marketplace Graveyard :: Validation, defect, P3)

Description

[Mathieu Pillard [:mat]]

The behaviour of the 'let' keyword has changed in Firefox 35: https://developer.mozilla.org/en-US/Firefox/Releases/35/Site_Compatibility#JavaScript

Bug 1001090 – Implement ES6 "temporal dead zone" for let and const

> The let statement implementation has been updated to support the "temporal dead zone"
> of the ECMAScript 6 spec, though the implementation is not yet fully ES6-compatible. 
> Starting with Firefox 35, redeclaring an existing variable in the same block scope 
> throws a TypeError, while referring a variable before the variable is declared raises
> a This change will mainly affect Open Web Apps for Firefox and Firefox OS, as well as
> Firefox extensions. See also the newsgroup announcement for details.

We can probably tweak the validator to throw a warning / error when it detects such uses.

Comment 1

[David Durst [:ddurst]]

Is this an issue for the validator? Does it check for scoping issues for variables?