Rules for When to Use useEffect in React

Purpose:
Guide coding agents to use useEffect only when appropriate, avoiding common pitfalls and misuse.

Rule: Use useEffect only for true side effects—operations that must happen outside the normal React render flow and cannot be handled by rendering logic, event handlers, or derived state.

When to Use useEffect

Use useEffect if your code needs to:

• Interact with external systems or APIs:

  • Fetching data from a server
  • Subscribing to WebSocket or event listeners
  • Setting up timers or intervals
  • Manually manipulating the DOM (rare, but sometimes necessary)[4][7]

• Synchronize with systems outside React:

  • Updating browser title or URL
  • Managing focus or scroll position
  • Integrating with third-party libraries that require manual setup/teardown[1][4]

• Clean up resources:

  • Remove event listeners
  • Cancel network requests
  • Clear timers or intervals when the component unmounts or dependencies change[4][2]

When Not to Use useEffect

Do not use useEffect for:

• Deriving state from props or other state:
  • If you can compute a value directly in render (e.g., filtering a list based on search input), do it inline or with a memoized value, not in an effect[5][6].
• Handling user events:
  • Use event handlers (e.g., onClick, onSubmit) directly, not effects triggered by state changes[1][6].
• Synchronizing state changes:
  • Prefer derived/computed state or useMemo for calculations based on other state[3][5].
• Triggering effects that could be handled by React’s rendering:
  • If you’re only updating UI in response to state/props, let React handle it[6].

Best Practices

• Always provide a correct dependency array:
  • List all reactive values used inside the effect[3][6].
• Split effects by concern:
  • Use multiple useEffect hooks for unrelated side effects[4][6].
• Use cleanup functions:
  • Clean up subscriptions, timers, or listeners to avoid memory leaks[4][2].
• Avoid unnecessary state:
  • Don’t store derived data in state just to trigger effects—compute it during render if possible[5][6].

Quick Decision Table

| Situation | Use useEffect? | Alternative | |----------------------------------------------|:----------------:|---------------------------| | Fetching data from API on mount | Yes | — | | Setting up event listeners | Yes | — | | Filtering a list based on search input | No | Compute in render | | Handling form submission | No | Use event handler | | Updating document title | Yes | — | | Synchronizing two pieces of state | No | Derived/computed state |

Summary

Use useEffect only for side effects that cannot be achieved by rendering logic, event handlers, or derived state. If you’re tempted to use useEffect for something that can be handled during render, reconsider your approach[3][5][6].

By following this rule, you’ll write cleaner, more predictable React code and avoid the common pitfalls associated with unnecessary or misused effects.

Sources [1] A complete guide to the useEffect React Hook - LogRocket Blog https://blog.logrocket.com/useeffect-react-hook-complete-guide/ [2] Rules of React's useEffect - CoderPad https://coderpad.io/blog/development/rules-of-reacts-useeffect/ [3] Mastering useEffect: Rules, Best Practices, and Pitfalls https://dev.to/cybermaxi7/mastering-useeffect-rules-best-practices-and-pitfalls-353e [4] ReactJS useEffect Hook - GeeksforGeeks https://www.geeksforgeeks.org/reactjs-useeffect-hook/ [5] Best Practices for useState and useEffect in React - DEV Community https://dev.to/wdp/best-practices-for-usestate-and-useeffect-in-react-4aea [6] The ultimate guide to using the useEffect hook in React - Zipy.ai https://www.zipy.ai/blog/useeffect-hook-guide [7] Using the Effect Hook - React https://legacy.reactjs.org/docs/hooks-effect.html [8] useEffect - React https://react.dev/reference/react/useEffect [9] UseEffect Best Practices : r/reactjs - Reddit https://www.reddit.com/r/reactjs/comments/18l98mh/useeffect_best_practices/ [10] A Deep Dive into useEffect: Best Practices for React Developers https://dev.to/hkp22/a-deep-dive-into-useeffect-best-practices-for-react-developers-3b93 [11] Understanding React hook useEffect & best practice - Stack Overflow https://stackoverflow.com/questions/66267135/understanding-react-hook-useeffect-best-practice [12] Understanding useEffect() : r/react - Reddit https://www.reddit.com/r/react/comments/tivs7z/understanding_useeffect/ [13] You Might Not Need an Effect - React https://react.dev/learn/you-might-not-need-an-effect [14] Rules of Hooks - React https://legacy.reactjs.org/docs/hooks-rules.html [15] Clean Code Hack: A Short Guide to useEffect Usage in React https://itnext.io/clean-code-hack-a-short-guide-to-useeffect-usage-in-react-a0a75d189fdc [16] What is the good practice to use React.JS useEffect hook for multiple ... https://stackoverflow.com/questions/68713509/what-is-the-good-practice-to-use-react-js-useeffect-hook-for-multiple-states [17] When to use useEffect? - reactjs - Stack Overflow https://stackoverflow.com/questions/57003084/when-to-use-useeffect [18] React useEffect() - A complete guide - Hygraph https://hygraph.com/blog/react-useeffect-a-complete-guide [19] React useEffect: A complete guide with examples - DeadSimpleChat https://deadsimplechat.com/blog/react-useeffect-a-complete-guide-with-examples/ [20] React useEffect Hooks - W3Schools https://www.w3schools.com/react/react_useeffect.asp