React Useeffect

by davila78da17d671b6fNo license32K starsListed Oct 8, 2026Updated Oct 8, 2026Repository updated today

React useEffect best practices from official docs. Use when writing/reviewing useEffect, useState for derived values, data fetching, or state synchronization. Teaches when NOT to use Effect and better alternatives.

Instructions onlySoftware Development

AI-generated overview

Guides React developers on when to use or avoid useEffect, with alternatives for derived state, events, and data fetching.

What it does: This skill provides React useEffect best practices drawn from official documentation. It explains that Effects are an escape hatch for synchronizing with external systems and lists situations where they are unnecessary. It includes a quick-reference table, a decision tree, and links to anti-patterns and alternative approaches such as useMemo, key props, and useSyncExternalStore.
When to use it: Use it when writing or reviewing React components that involve useEffect, useState for derived values, data fetching, or state synchronization. It is also useful when deciding whether an Effect is needed at all.
Requirements: No tools, packages, or credentials are required; it is instructions only and ships no scripts.

You Might Not Need an Effect

Effects are an escape hatch from React. They let you synchronize with external systems. If there is no external system involved, you shouldn't need an Effect.

Quick Reference

Situation	DON'T	DO
Derived state from props/state	`useState` + `useEffect`	Calculate during render
Expensive calculations	`useEffect` to cache	`useMemo`
Reset state on prop change	`useEffect` with `setState`	`key` prop
User event responses	`useEffect` watching state	Event handler directly
Notify parent of changes	`useEffect` calling `onChange`	Call in event handler
Fetch data	`useEffect` without cleanup	`useEffect` with cleanup OR framework

When You DO Need Effects

Synchronizing with external systems (non-React widgets, browser APIs)
Subscriptions to external stores (use useSyncExternalStore when possible)
Analytics/logging that runs because component displayed
Data fetching with proper cleanup (or use framework's built-in mechanism)

When You DON'T Need Effects

Transforming data for rendering - Calculate at top level, re-runs automatically
Handling user events - Use event handlers, you know exactly what happened
Deriving state - Just compute it: const fullName = firstName + ' ' + lastName
Chaining state updates - Calculate all next state in the event handler

Decision Tree

Need to respond to something?├── User interaction (click, submit, drag)?│   └── Use EVENT HANDLER├── Component appeared on screen?│   └── Use EFFECT (external sync, analytics)├── Props/state changed and need derived value?│   └── CALCULATE DURING RENDER│       └── Expensive? Use useMemo└── Need to reset state when prop changes?    └── Use KEY PROP on component

Need to respond to something?├── User interaction (click, submit, drag)?│   └── Use EVENT HANDLER├── Component appeared on screen?│   └── Use EFFECT (external sync, analytics)├── Props/state changed and need derived value?│   └── CALCULATE DURING RENDER│       └── Expensive? Use useMemo└── Need to reset state when prop changes?    └── Use KEY PROP on component

Detailed Guidance

Anti-Patterns - Common mistakes with fixes
Better Alternatives - useMemo, key prop, lifting state, useSyncExternalStore

Source and attribution

Source:davila7/claude-code-templatesincli-tool/components/skills/development/react-useeffectat commit8da17d6

License: No license

Content belongs to its original authors. SourceWeft indexes it from a public repository.

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React Useeffect

You Might Not Need an Effect

Quick Reference

When You DO Need Effects

When You DON'T Need Effects

Decision Tree

Detailed Guidance

Source and attribution

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