filterElementsFromArray.ts

/*

Given an integer array arr and a filtering function fn, return a filtered array filteredArr.

The fn function takes one or two arguments:

arr[i] - number from the arr
i - index of arr[i]
filteredArr should only contain the elements from the arr for which the expression fn(arr[i], i) evaluates to a truthy value. A truthy value is a value where Boolean(value) returns true.

Please solve it without the built-in Array.filter method.

*/

type Fn = (n: number, i: number) => any;

function filter(arr: number[], fn: Fn): number[] {
  const filtered: number[] = [];
  arr.forEach((v, i) => {
    if (!!fn(v, i)) {
      filtered.push(v);
    }
  });

  return filtered;
}