Promise执行控制

const p1 = new Promise((resolve) => {
  setTimeout(() => {
    resolve(1);
  }, 1000);
});
const p2 = new Promise((resolve,reject) => {
  setTimeout(() => {
    // resolve(2);
    reject(2);
  }, 2000);
});
const p3 = new Promise((resolve) => {
  setTimeout(() => {
    resolve(3);
  }, 3000);
});
const promiseArr = [p1, p2, p3];

多个请求继发执行

https://libin1991.github.io/2019/04/17/%E4%B8%BA%E5%95%A5await%E4%B8%8D%E8%83%BD%E7%94%A8%E5%9C%A8forEach%E4%B8%AD/

(async function test() {
  for (const p of promiseArr) {
    const res = await p;
    console.log(res);
  }
})();
// 顺序打印出
1
2
3
// 如果有个promise错误 ,会中断
// 需要catch
(async function test() {
  const res = [];
  for (const p of promiseArr) {
    const a = await p.catch((err) => err);
    console.log(a)
    res.push(a); //可以用数组存起来结果
  }
  console.log(res); // [1,2,3]
})();

多个请求并发执行

Promise.all(promiseArr)
  .then((res) => {
    console.log("res", res); // 3s后一下打印出 [1, 2, 3]
  })
  .catch((err) => {
    console.log("err", err);
  });
// 如果有个promise错误也会中断
// 返回一个处理之后的promise数组，让所有的promises都走resolve
const transPromises = (promises) => {
  return promises.map((promise) => {
    return promise.then((res) => res).catch((err) => err);
  });
};
const newArr = transPromises(promiseArr);
Promise.all(newArr)
  .then((res) => {
    console.log("res", res);
  })
  .catch((err) => {
    console.log("err", err);
  });
// res [ 1, 'e2', 3 ]

Promise.allSettled

Promise.allSettled(promiseArr)
  .then((res) => {
    console.log("res", res);
  })
  .catch((err) => {
    console.log("err", err);
  });
// 打印：
res [
  { status: 'fulfilled', value: 1 },
  { status: 'rejected', reason: 'e2' },
  { status: 'fulfilled', value: 3 }
]