js-set-map-lookups
Convert arrays to Set/Map for repeated membership checks.
- Skills
- Web development
- 0
What it does and how to use it
A skill that teaches Claude Code to do web development tasks well. It is packaged knowledge the model uses whenever it is relevant.
- Install the skill (command above).
- In Claude Code, describe what you need - the skill turns on by itself when the context fits.
- No commands to memorize: you talk in plain language and the skill does the rest.
Install (Claude Code)
mkdir -p .claude/skills/js-set-map-lookups && curl -fsSL https://doutorai.pt/data/lib/skills__js-set-map-lookups.md -o .claude/skills/js-set-map-lookups/SKILL.mdPaste this command into the terminal, in your project folder, and the component installs automatically.
Content
---
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))
```
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