Keep Even Numbers

Arrays of numbers are common, and filtering by a simple predicate is a great starting point. Here you’ll use filter with a small helper to keep only even numbers. The result should be a new number[].

This problem reinforces reading from a number[], writing a boolean-returning predicate, and returning a new array without mutating the input.

Your Task

• Complete the function isEven(n: number): boolean.
• Complete the function keepEven(nums: number[]): number[] using isEven.
• Do not mutate the input array.

Examples

• keepEven([1, 2, 3, 4, 5]) → [2, 4]
• keepEven([]) → []