lodash/lodash

`meanBy` returning `NaN` on empty lists is error prone

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#5,901 opened on Jul 10, 2024

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Description

_.meanBy([], 'test') will return NaN

This behavior is not currently documented, meaning that users might not know that it could return NaN.

Possible solutions:

  • Make meanBy return undefined instead of NaN, meaning that users using TypeScript will have to handle that case
  • Improve the documentation to warn users that they mustn't assume that the returned value is a valid number

Contributor guide

Research direction
Inspect the current implementation of meanBy in the source code, check how other similar functions handle empty arrays (e.g., mean, sumBy), and consider the impact of returning undefined vs NaN. Review existing tests and documentation.
Tech stack
javascript
Domain
backendfrontend
Issue type
Bug
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.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaScriptGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70