sindresorhus/type-fest

Remove redundant code for compatibility with older versions of typescript

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#1,142 opened on May 16, 2025

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enhancementgood first issue

Description

In some previously supported but now unsupported versions of typescript, there would be some incorrect circular check, and in order to bypass the circular check, we have to add some non-essential code, for example:

type A<T> = 
 SomeToolType<T> extends infer B 
  ? B
  : never // Never happen

The above code can be simplified now:

type A<T> = SomeToolType<T>

Contributor guide

Tech stack
typescript
Domain
toolingdeveloper experience
Issue type
refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
familiarity with TypeScript genericsunderstanding of type fest patterns
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85
Research direction
Search the codebase for patterns like `SomeToolType<T> extends infer B ? B : never` where the conditional type is unnecessary due to removed support for older TypeScript versions. Look in source type definitions for such redundant patterns and simplify them to directly use `SomeToolType<T>`. The issue provides an example; apply similar logic to other occurrences. Check the repository's CONTRIBUTING.md for contribution guidelines.
Remove redundant code for compatibility with older versions of typescript · sindresorhus/type-fest#1142 | Good First Issue