What is React Strict Mode and why should you use it

· Category: React

Short answer

Strict Mode is a development-only wrapper that intentionally double-invokes certain functions to help detect impure renderers and missing cleanup logic.

How it works

In development, React mounts components twice, runs effects twice, and warns about deprecated APIs. This surfaces bugs that might otherwise only appear in production under concurrent features.

Example

<StrictMode>
  <App />
</StrictMode>

Why it matters

  • Helps identify components with side effects during render.
  • Detects missing key props in lists.
  • Prepares your codebase for future React features like Concurrent Mode and Server Components.

Tips

  • Do not suppress Strict Mode warnings; fix the root cause.
  • Ensure all effects have proper cleanup functions.
  • It has no impact on production bundles.