client-passive-event-listeners

---
title: Use Passive Event Listeners for Scrolling Performance
impact: MEDIUM
impactDescription: eliminates scroll delay caused by event listeners
tags: client, event-listeners, scrolling, performance, touch, wheel
---

## Use Passive Event Listeners for Scrolling Performance

Add `{ passive: true }` to touch and wheel event listeners to enable immediate scrolling. Browsers normally wait for listeners to finish to check if `preventDefault()` is called, causing scroll delay.

**Incorrect:**

```typescript
useEffect(() => {
  const handleTouch = (e: TouchEvent) => console.log(e.touches[0].clientX)
  const handleWheel = (e: WheelEvent) => console.log(e.deltaY)
  
  document.addEventListener('touchstart', handleTouch)
  document.addEventListener('wheel', handleWheel)
  
  return () => {
    document.removeEventListener('touchstart', handleTouch)
    document.removeEventListener('wheel', handleWheel)
  }
}, [])
```

**Correct:**

```typescript
useEffect(() => {
  const handleTouch = (e: TouchEvent) => console.log(e.touches[0].clientX)
  const handleWheel = (e: WheelEvent) => console.log(e.deltaY)
  
  document.addEventListener('touchstart', handleTouch, { passive: true })
  document.addEventListener('wheel', handleWheel, { passive: true })
  
  return () => {
    document.removeEventListener('touchstart', handleTouch)
    document.removeEventListener('wheel', handleWheel)
  }
}, [])
```

**Use passive when:** tracking/analytics, logging, any listener that doesn't call `preventDefault()`.

**Don't use passive when:** implementing custom swipe gestures, custom zoom controls, or any listener that needs `preventDefault()`.