AI agent skill · by @TheOrcDev

Js Set Map Lookups

Use Set and Map for O(1) membership lookups instead of array.includes(). Apply when checking membership repeatedly or performing frequent lookups against a collection.

Archived 2026-10-23 · Source updated 2026-10-08 · License: MIT. Check the original repository for the latest version.

SKILL.md instructions

## 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))
```