Event Delegation Performance Benefits
Why event delegation is better for performance with many elements.
Event Delegation Performance Benefits
Memory
- Individual: 100 items = 100 listeners = 100 closures in memory.
- Delegation: 100 items = 1 listener = 1 closure in memory.
Initialization Time
- Individual: 100 addEventListener calls on page load.
- Delegation: 1 addEventListener call on page load.
Dynamic Elements
- Individual: each new element needs addEventListener (extra work).
- Delegation: new elements work automatically (no extra work).
Event Handling Speed
- Individual: direct handler call (fastest).
- Delegation: checks e.target on every click (slightly slower, but negligible).
When Performance Matters
For 1000+ items, delegation is significantly better. For < 20 items, the difference is negligible.
The Takeaway
Delegation is better for performance: less memory (1 listener vs 100), faster initialization (1 addEventListener vs 100), and no extra work for dynamic elements. The per-click overhead (e.target check) is negligible. Use delegation for 20+ items.
Less memory (1 listener and 1 closure vs 100), faster initialization (1 addEventListener vs 100), and no extra work for dynamically added elements. The per-click overhead (e.target check) is negligible.
For 100 items: individual listeners use 100 closures (one per listener). Delegation uses 1 closure. For 1000 items: 1000 vs 1. The memory savings scale with the number of items.
Slightly. Delegation checks e.target on every click (a matches() or closest() call). But this is negligible compared to the memory and initialization savings. For 20+ items, delegation is almost always better.
For 20+ similar items, use delegation. For < 20 items, individual listeners are fine. The exact threshold depends on the use case, but 20 is a reasonable cutoff.
Yes. One addEventListener call is faster than 100. For 1000 items, the initialization time difference is noticeable. Delegation also avoids the need to re-add listeners when the DOM changes.
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