EJ: C4 P1 created by oliverjam - https://repl.it/ESBy/1

EJ: C4 P1.js

function range(start, end, step) {
  let result = [];
  if (step === undefined && start < end) {
  	step = 1
  } else if (step === undefined && start > end) {
  	step = -1;
  }
  if (step < 0) {
    for (let i = start; i>= end; i += step) {
		result.push(i);
    }
  } else {
    for (let i = start; i <= end; i += step) {
      result.push(i);
    }
  }
  return result;
}

function sum(arr) {
	return arr.reduce((prev, curr) => prev + curr);
}

console.log(range(5, 2));
console.log(range(1, 10));
console.log(range(5, 2, -1));
console.log(range(1, 10, 2));
console.log(sum(range(1, 10)));