Iterator Protocol: Array

const arr = [1, 2, 3]
const iter = arr[Symbol.iterator]()
console.log(iter.next()) // → { value: 1, done: false }
console.log(iter.next()) // → { value: 2, done: false }
console.log(iter.next()) // → { value: 3, done: false }

The iterator protocol requires an object to implement a next() method returning { value, done } objects.