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Rerender Move Effect To Event

Source: .agents/references/coding-standard/vercel-react-best-practices/rules/rerender-move-effect-to-event.md

Metadata​

  • title: Put Interaction Logic in Event Handlers
  • impact: MEDIUM
  • impactDescription: avoids effect re-runs and duplicate side effects
  • tags: rerender, useEffect, events, side-effects, dependencies

Content​

Put Interaction Logic in Event Handlers​

If a side effect is triggered by a specific user action (submit, click, drag), run it in that event handler. Do not model the action as state + effect; it makes effects re-run on unrelated changes and can duplicate the action.

Incorrect (event modeled as state + effect):

function Form() {
  const [submitted, setSubmitted] = useState(false)
  const theme = useContext(ThemeContext)

  useEffect(() => {
    if (submitted) {
      post('/api/register')
      showToast('Registered', theme)
    }
  }, [submitted, theme])

  return <button onClick={() => setSubmitted(true)}>Submit</button>
}

Correct (do it in the handler):

function Form() {
  const theme = useContext(ThemeContext)

  function handleSubmit() {
    post('/api/register')
    showToast('Registered', theme)
  }

  return <button onClick={handleSubmit}>Submit</button>
}

Reference: Should this code move to an event handler?