sindresorhus/type-fest

Add `Truthy` and `Falsy` types

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#394 opened on Apr 30, 2022

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 (4 comments) (8 reactions) (0 assignees)TypeScript (471 forks)batch import
corehelp wantedtype addition

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Description

The implementation seems pretty straightforward:

type Falsy = Zero | "" | false | null | undefined;
type Truthy<T = Numeric | object | string | symbol | true> = Exclude<T, Falsy>;

Falsy should include NaN, but TypeScript does not provide that at the type level.

Technically, Falsy should also include HTMLAllCollection due to the [[IsHTMLDDA]] internal slot. However, that type is only available for DOM code (not NodeJS) and is deprecated anyways, so I think it's okay to exclude it from this union.

Contributor guide

Research direction
Implement the Truthy and Falsy types as described, ensuring they work with the existing type system. Test edge cases like excluding NaN and HTMLAllCollection.
Tech stack
typescript
Domain
backend
Issue type
Feature
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.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80