Array.filter()

Runs a test on every element and returns a new array of only the ones that passed.

Calls the callback for each element; if the callback returns truthy, the element is included in the new array. Does not mutate. The result may be shorter than the original (or empty).

A selection operation over a collection. O(n) time, O(k) space where k is the number of matching elements. Often chained with .map() to select-then-transform.