text: let fibonacci = {
    [Symbol.iterator]() {
      let pre = 0;
      let cur = 1;
  
      return {
        next() {
          [pre, cur] = [cur, pre + cur];
          return { done: false, value: cur };
        }
      };
    }
  };
  
  for (let n of fibonacci) {
    if (n > 1000) {
      break;
    }
    console.log(n);
  }
  