cssinjs/jss

themed useCreateStyles creates className mismatch when hydrating in StrictMode

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#1338 opened on Apr 26, 2020

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bughelp wanted

Description

Expected behavior: className matches during hydration

Describe the bug: The counter in the className is off by one

Codesandbox link: https://codesandbox.io/s/createusestyles-classname-mismatch-zdojq?file=/src/App.js

The useLayoutEffect warnings are false positives since we SSR in the browser to showcase the issue better. Versions (please complete the following information):

  • jss: 10.1.1
  • Browser [e.g. chrome, safari]: Chrome 81
  • OS [e.g. Windows, macOS]: ubuntu 18.04
  • react: 16.13.1

Contributor guide

Tech stack
javascriptreact
Domain
frontend
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 hydration knowledgeCSS in JS basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Investigate the className counter logic in JSS's createUseStyles hook, likely in packages/jss/src/createUseStyles.js. The codesandbox demonstrates a mismatch during hydration, so focus on how class names are generated and incremented across server and client renders. Check if the counter resets incorrectly in React StrictMode double rendering.