range.js

function range(s, e) {
  let start
  let end
  if (e == null) {
    end = s
    start = 0
  } else {
    start = s
    end = e
  }
  return {
    [Symbol.iterator]() {
      return {
        next: () => {
          if (start < end) {
            return { value: start++, done: false };
          } else {
            this.index = start; //If we would like to iterate over this again without forcing manual update of the index
            return { done: true };
          }
        }
      }
    }
  }
}


for (const i of range(10)) {
  console.log(i);
}
for (const i of range(1, 10)) {
  console.log(i);
}
[...range(10)].map(i => console.log(i))