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contains ​

Problem ​

You need to check whether an array includes a value, optionally using a selector for comparison instead of strict reference equality.

Solution ​

Use contains(array, value, selector?) to check membership. Without a selector it uses deep equality; with a selector it compares projected keys.

ts
import { contains } from '@vielzeug/arsenal';

contains([1, 2, 3], 2); // true
contains([1, 2, 3], 4); // false

const users = [{ id: 1 }, { id: 2 }];
contains(users, { id: 2 }, (u) => u.id); // true

Pitfalls ​

  • Without a selector, uses deep equality — may be slower for large objects. Use a selector for performance when comparing by key.