evenify

let beforeInts = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 100, 112, 113];
let afterInts = evenify(beforeInts);

console.log('beforeInts: ' + beforeInts);
console.log('afterInts: ' + afterInts);

function evenify(ints, currentIndex = 0, evenInts = []) {// es6 feature for default argument values
  let currentInt = ints[currentIndex];
  if (currentInt % 2 === 0) {
    evenInts.push(currentInt);
  }
  if (++currentIndex >= ints.length) {
    return evenInts;
  } 
  return evenify(ints,  currentIndex,  evenInts) ;
}