Microsoft/TypeScript

Improve errors for potential arrow functions

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#25,898 opened on Jul 24, 2018

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 (1 comment) (0 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
BugDomain: Error MessagesEffort: ModerateHelp Wanted

Description

There are certain locations where arrow functions don't parse

var x = window.foo || () => {}

In these instances, it would be nice if users could get a better error message as to avoid issues like #25897.

Ideally this should not be an invasive change.

  • The change should be limited in scope.
  • The parser should continue erroring in those locations.
  • The change must not introduce change how existing valid code is parsed.

Contributor guide

Tech stack
typescript
Domain
toolingdeveloper experience
Issue type
feature
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.
1-3 hours
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
TypeScript parser internalserror message generation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the parser's error handling in locations where arrow functions are not allowed (e.g., after ||). Look at the current error messages for syntax errors in those contexts and determine how to provide more specific hints about possible arrow function use. Check issue #25897 for related context. Ensure changes are minimal and do not affect valid code parsing.