js-set-map-lookups

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))