js set map lookups

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):

const allowedIds = ['a', 'b', 'c', ...]
items.filter(item => allowedIds.includes(item.id))

Correct (O(1) per check):

const allowedIds = new Set(['a', 'b', 'c', ...])
items.filter(item => allowedIds.has(item.id))

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