var arrayOfLight = function (x) {
  // note that x must be a positive number
  // prints from 0 to that number
  var result = [];
  for (var i = 0; i <= x; i++) {
    result.push(i);
  }
  
  return result;
};

var response = arrayOfLight(5); // = [0, 1, 2, 3, 4, 5]
console.log(response);