// finds the armstrong numbers below n
function armstrong(n) {
  var str = String(n);

  // create an array of numbers from the components
  // ex: 154 -> [1, 5, 4]
  var numbers = str.split('').map(Number);

  // create an array of cubes
  // ex: [1, 125, 64]
  var cubes = numbers.map(num => Math.pow(num, 3));

  // sum all the values:
  var sum = cubes.reduce((a,b) => a + b, 0);

  return sum === n;
}