React useEffect Cleanup Explained: Timers, Event Listeners, and Fetch Race Conditions

SitePoint has published a guide to how useEffect cleanup works in React, focusing on three common sources of bugs: fetch race conditions, intervals, and event listeners. It includes code patterns, lifecycle explanations, and a checklist for pull request reviews.

The three cases it covers

Anyone who writes React components regularly will recognize all three. Intervals and event listeners can keep running if they aren't cleaned up when a component changes or unmounts. Fetch has a different problem: race conditions, where several requests overtake each other. The cleanup function in useEffect is the place to tidy all of that up.

According to the source summary, the guide covers:

• How the cleanup function handles fetch race conditions
• How to deal with intervals and event listeners
• Code patterns you can study right away
• Lifecycle explanations behind how cleanup works
• A checklist for PR reviews

A PR review checklist for teams

The most practical part may be the PR review checklist. Bugs from missed cleanup often only show up after an app has been running for a while, so a checklist during code review can catch them earlier. The source summary doesn't detail what the checklist contains, so you'll need to read the full article on SitePoint for specifics.

If you or your team build apps with React, this guide is worth using as a discussion topic or a reference for your internal code review standards.