Skip to main content

Rerender Dependencies

Source: .agents/references/coding-standard/vercel-react-best-practices/rules/rerender-dependencies.md

Metadata​

  • title: Narrow Effect Dependencies
  • impact: LOW
  • impactDescription: minimizes effect re-runs
  • tags: rerender, useEffect, dependencies, optimization

Content​

Narrow Effect Dependencies​

Specify primitive dependencies instead of objects to minimize effect re-runs.

Incorrect (re-runs on any user field change):

useEffect(() => {
  console.log(user.id)
}, [user])

Correct (re-runs only when id changes):

useEffect(() => {
  console.log(user.id)
}, [user.id])

For derived state, compute outside effect:

// Incorrect: runs on width=767, 766, 765...
useEffect(() => {
  if (width < 768) {
    enableMobileMode()
  }
}, [width])

// Correct: runs only on boolean transition
const isMobile = width < 768
useEffect(() => {
  if (isMobile) {
    enableMobileMode()
  }
}, [isMobile])