4 · Build useful programs · 9 MIN

Select matching items

Filtering keeps items that meet a rule.

A predicate is a function returning true or false. filter calls it for each item and creates a new array containing the matches. The original array stays unchanged. This scans n items in O(n) time and stores up to n matches.

A sieve keeps only the items that fit a rule.

Read the example

const scores = [30, 60, 90];
const passed = scores.filter(n => n >= 60);
console.log(JSON.stringify(passed));

[60,90]

Your challenge

Return a new array containing only the even numbers from input, preserving order.

Common trap

Use === for comparison. = is assignment.