For await of

function Gen(time) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(time);
    }, time);
  });
}
// async function test() {
//   let arr = [Gen(2000), Gen(100), Gen(3000)];
//   for (let item of arr) {
//     console.log(Date.now(), await item.then(console.log));
//   }
// }
// test();
// async function test() {
//   let arr = [Gen(2000), Gen(100), Gen(3000)];
//   for await (let item of arr) {
//     console.log(Date.now(), item);
//   }
// }
// test();
const obj = {
  count: 0,
  Gen(time) {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve({ done: false, value: time });
      }, time);
    });
  },
  [Symbol.asyncIterator]() {
    let self = this;
    return {
      next() {
        self.count++;
        if (self.count < 4) {
          return self.Gen(Math.random() * 1000);
        } else {
          return Promise.resolve({
            done: true,
            value: ""
          });
        }
      }
    };
  }
};
async function test() {
  for await (let item of obj) {
    console.log(Date.now(), item);
  }
}
test();