js-set-map-lookups

Original：🇺🇸 English

Translated

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.

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Sourcetheorcdev/8bitcn-ui

Added on2026-02-20

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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))

js-set-map-lookups

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SKILL.md Content

Use Set/Map for O(1) Lookups