ES6 Iterators and Generators

iterators.js

let fib = {
  [Symbol.iterator]() {
    let pre = 0, cur = 1;
    return {
      next() {
        [pre, cur] = [cur, pre + cur];
        return { done: false, value: cur }
      }
    }
  }
}

let fibGen = {
  [Symbol.iterator]: function*() {
    let pre = 0, cur = 1;
    for (;;) {
      [pre, cur] = [cur, pre + cur];
      yield cur;
    }
  }
}

//for (var n of fibGen) {
//  if (n > 10000) { break; }
//  console.log(n);
//}

for (var x of fibGen) {
  if (x > 1000) { break; }
  console.log(x)
}