chakra-core/ChakraCore

No syntax error for let redeclaring var in a block

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#849 opened on Apr 21, 2016

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 (3 comments) (0 reactions) (0 assignees)JavaScript (9,000 stars) (1,374 forks)batch import
BugSeverity: 3help wanted

Description

{ var x; let x; }

Expected: SyntaxError, duplicate delcarations. Actual: No error, var is hoisted out.

Contributor guide

Tech stack
javascriptcpp
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaScript scopingChakraCore parser internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Investigate the parser's handling of block scoped declarations, specifically in the file(s) responsible for parsing variable declarations (e.g., Parser.cpp). The issue is that redeclaring a var with let in a block does not produce a SyntaxError. Trace the logic for hoisting and duplicate declaration checks. Refer to test cases in the repository to ensure the fix does not break other scenarios.