Implementing your own Generator using closure !!!

Here is a small program generating x to y numbers using generator in JS later we will implement equivalent function by using closure.

Generating x to y numbers using Generator

function* genXtoY(x, y) {
  while (x < y) yield x++
  return x++
}

const _iter = genXtoY(1, 5)

_iter.next() //{ value: 1, done: false }
_iter.next() //{ value: 2, done: false }
_iter.next() //{ value: 3, done: false }
_iter.next() //{ value: 4, done: false }
_iter.next() //{ value: 5, done: true }
_iter.next() //{ value: undefined, done: true }

Generating x to y numbers using closure

const genXtoY = (x, y) => {
  const next = () => {
    if (x <= y) return { value: x++, done: x - 1 === y }

    return { value: undefined, done: true }
  }
  return { next }
}

const _iter = genXtoY(1, 5)

_iter.next() //{ value: 1, done: false }
_iter.next() //{ value: 2, done: false }
_iter.next() //{ value: 3, done: false }
_iter.next() //{ value: 4, done: false }
_iter.next() //{ value: 5, done: true }
_iter.next() //{ value: undefined, done: true }