题目描述

请你实现Promise.allSettled

一句话概括就是👇

等到传入Promise数组所有的的promise都执行完毕了，返回一个Promise，它的resolve中包含所有返回结果的对象数组

• 返回成功的对象就是resolve: {status: "fulfilled", value: "xx"}
• 返回失败的对象就是 reject: {status: "rejected", reason: "xx"}

如果传入参数数组为空，就返回空数组

MDN上的描述

Promise. allsettle()静态方法接受Promise的可迭代对象作为输入，并返回一个Promise。当所有输入的promise都完成时(包括传递空可迭代对象时)，这个返回的promise就会完成，并使用一个对象数组来描述每个promise的结果 —— resolve(resArr)

代码实现

const allSettled = function (promises) {
  // 返回一个对象数组
  // resolve: {status: "fulfilled", value: "xx"}
  // reject: {status: "rejected", reason: "xx"}
  let res = [];
  if (promises.length === 0) {
    return res;
  }

  return new Promise((resolve) => {
    let len = promises.length;
    promises.forEach((item, index) => {
      Promise.resolve(item).then(
        (value) => {
          res[index] = {
            status: "fulfilled",
            value,
          };
          len--;
          if (len === 0) {
            resolve(res);
          }
        },
        (reason) => {
          res[index] = {
            status: "rejected",
            reason,
          };
          len--;
          if (len === 0) {
            resolve(res);
          }
        }
      );
    });
  });
};
const p1 = new Promise((resolve) => {
  setTimeout(() => {
    resolve(2);
  }, 3000);
});
const p2 = Promise.reject("error");
const p3 = new Promise((resolve) => {
  setTimeout(() => {
    resolve("5");
  }, 1000);
});
const p4 = new Promise((resolve) => {
  setTimeout(() => {
    resolve("4");
  }, 2000);
});
const p5 = 5;

allSettled([p1, p2, p3, p5]).then((res) => console.log("2: ", res));

/* 
  2:  [
    { status: 'fulfilled', value: 2 },
    { status: 'rejected', reason: 'error' },
    { status: 'fulfilled', value: '5' },
    { status: 'fulfilled', value: 5 }
  ]
*/