code: function range(start, stop, step) {
    if (start != null && typeof start != 'number') {
      throw new Error('start must be a number or null');
    }
    if (stop != null && typeof stop != 'number') {
      throw new Error('stop must be a number or null');
    }
    if (step != null && typeof step != 'number') {
      throw new Error('step must be a number or null');
    }
    if (stop == null) {
      stop = start || 0;
      start = 0;
    }
    if (step == null) {
      step = stop > start ? 1 : -1;
    }
    var toReturn = [];
    var increasing = start < stop; //← here’s the change
    for (; increasing ? start < stop : start > stop; start += step) {
      toReturn.push(start);
    }
    return toReturn;
  }
docs: /*
  range(0, 5); // [0, 1, 2, 3, 4]
  range(5); // [0, 1, 2, 3, 4]
  range(-5); // [0, -1, -2, -3, -4]
  range(0, 20, 5) // [0, 5, 10, 15]
  range(0, -20, -5) // [0, -5, -10, -15]