generators.js

const data = [
  [1,2,3,4,5],
  [6,7,8,9,10]
]


function* getNumbers() {
  for(let idx in data) {
    for(let subIdx in data[idx]) {
      yield data[idx][subIdx]
    }
  }
}

const getNumber = getNumbers()

(function() {
  const aNumber = getNumber.next().value // getNumber().next() gives { value: 1, done: false }
  const anotherNumber = getNumber.next().value
  const yetAnotherNumber = getNumber.next().value
  console.log(aNumber, anotherNumber, yetAnotherNumber) // 1, 2, 3
})()