EcmaScript | ES6 iterators.js

const fibonacci = {
  // Iterated objects must implement [Symbol.iterator] method
  // which returns object with next method
  [Symbol.iterator]() {
    let pre = 0, cur = 1
    return {
      next() {
        [pre, cur] = [cur, pre + cur]
        return { done: false, value: cur }
      }
    }
  }
}

// It's possible to iterate with for/of loop
for (const n of fibonacci) {
  if (n > 100) break
  console.log(n)
}