React Useeffect

Skills development 127 Scanned by NVIDIA SkillSpector

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.

Install Command

npx claude-code-templates@latest --skill development/react-useeffect

View on GitHub

claude-code — react-useeffect

Scanned by NVIDIA SkillSpector

Automated static analysis (no LLM) · v2.12.0 · 2026-10-17

Partial analysis: some checks could not run on this component.

8 observations

scanner score 35/100

SkillSpector looks for patterns such as shell commands, credential access, network calls or unpinned dependencies. An observation is something worth reading in the files before you install, not a confirmed vulnerability. Components that run code locally, like hooks, MCP servers and security tooling, naturally show more of them.

Memory Manipulation ×4
Memory Poisoning · README.md:30
Memory Manipulation ×2
Memory Poisoning · SKILL.md:16
Memory Manipulation
Memory Poisoning · anti-patterns.md:55
Memory Manipulation
Memory Poisoning · alternatives.md:49

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Content

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

Detailed Guidance

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