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5chan/.codex/skills/vercel-react-best-practices/rules/js-set-map-lookups.md
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Tommaso CasaburiandGitHub a92b185a66 chore(ai-workflow): track repo-managed review tooling (#1046)
* chore(ai-workflow): track repo-managed review tooling

* fix(ai-workflow): remove repo-specific path assumptions

Make shared workflow hooks and APK testing guidance resolve paths from the repo and contributor environment so the tooling works for all contributors, not just one machine.
2026-03-10 15:49:15 +08:00

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---
title: Use Set/Map for O(1) Lookups
impact: LOW-MEDIUM
impactDescription: O(n) to O(1)
tags: javascript, set, map, data-structures, performance
---
## Use Set/Map for O(1) Lookups
Convert arrays to Set/Map for repeated membership checks.
**Incorrect (O(n) per check):**
```typescript
const allowedIds = ['a', 'b', 'c', ...]
items.filter(item => allowedIds.includes(item.id))
```
**Correct (O(1) per check):**
```typescript
const allowedIds = new Set(['a', 'b', 'c', ...])
items.filter(item => allowedIds.has(item.id))
```