range.step2.js

function range(start, end, step) {
  const results = [];
  
  if (end === undefined) {
    end = start;
    start = 0;
  }

  if (step === undefined) {
    step = (start < end) ? 1 : -1;
  }
  
  for (let num = start; (step > 0 && num < end) || (step < 0 && num > end); num += step) results.push(num);
  
  return results;
}