one fable-low hijack cell
pair fast / javascript
envelope en_arrow
ordering BA
effort low
English with arrow '→' — '{X} → {Y}'
verdictpicked javascript (second-offered)
· classifierB
· tiernone
response (200 chars)
# Fast JavaScript — Quick Tips
## Core Performance Wins
```javascript
// ✅ Use Maps/Sets for lookups — O(1) vs O(n)
const set = new Set(arr);
set.has(x); // fast
arr.includes(x);
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