welldone-software/why-did-you-render

Wdyr ignores equality function in useSelector

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#190 opened on Apr 16, 2021

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Low prioritybuggood first issuehelp wanted

Description

When using wdyr I noticed that it reports unnecessary renders caused by useSelector with an equality function even though the equality function causes the render to be avoided. Looking at the code it looks like wdyr does not consider the result of the equality function.

An example:

useSelector(someSelector, (prev, next) => true);

Contributor guide

Tech stack
javascriptreact
Domain
frontenddeveloper experience
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.
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
React basicsunderstanding of useSelectorfamiliarity with wdyr
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Start by locating the code in the why did you render repository that tracks renders and detects unnecessary re renders. Specifically, look for how useSelector is patched and where the equality function is called. The issue suggests that the equality function's result is ignored. Investigate the patch logic in files like 'trackHooks.js' or similar. Check the existing comments and any linked PRs for additional context. Confirm that the equality function result is not considered and then implement a fix that respects it.