function* gen() {
  yield  '1';
  yield  '2';
  yield  '3';
}

const a = gen();  //  這一步不能省略，很重要，如果a消費完了，你要重新獲取就const b = gen() 繼續(xù)next()

 console.log(a.next());
 console.log(a.next());
 console.log(a.next());
 console.log(a.next());

//  遍歷
 for (const b of gen()) {
   console.log(b);
}

模擬異步變同步

function* gen() {
  const d1 = yield data1();
  const d2 = yield data2();
  console.log(d1);
  console.log(d2);
}

const generator = gen();

const data1 = () => {
  setTimeout(() => {
    generator.next('11111');
  }, 2000);
};

const data2 = () => {
  setTimeout(() => {
    generator.next('2222');
  }, 1000);
};

generator.next();