【Promise.allSettled】手写Promise.allSettled方法

Promise.allSettled是Promise对象的一个静态方法
参数是一个可迭代对象，一般是一个Promise数组
该Promise.allSettled()方法返回一个Promise对象，当所有给定的 promise对象都已经fulfilled或rejected后，返回的Promise对象能拿到一个对象数组，每个对象表示对应的 promise 结果数据以及状态。

当您有多个彼此不依赖的异步任务成功完成时，或者您总是想知道每个promise的结果时，通常使用它。

const pro = new Promise((resolve, reject) => {
    
  setTimeout(() => {
    
    reject(3);
  }, 1000);
});
Promise.allSettled([pro, Promise.resolve(1), Promise.reject(2)]).then(
  (data) => {
    
    console.log(data);
  }
);

打印结果

[
  { status: 'rejected', reason: 3 },
  { status: 'fulfilled', value: 1 },
  { status: 'rejected', reason: 2 }
]

手写Promise.allSettled代码

Promise.myAllSettled = function (proms) {
    
  return new Promise((resolve, reject) => {
    
    let resolvedCount = 0;
    let count = 0;
    const results = [];
    for (const prom of proms) {
    
      let i = count;
      count++;
      Promise.resolve(prom)
        .then(
          (data) => {
    
            resolvedCount++;
            results[i] = {
    
              status: "fullfilled",
              value: data,
            };
          },
          (reason) => {
    
            resolvedCount++;
            results[i] = {
    
              status: "rejected",
              reason,
            };
          }
        )
        .finally(() => {
    
          if (resolvedCount >= count) {
    
            resolve(results);
          }
        });
    }
  });
};

const pro = new Promise((resolve, reject) => {
    
  setTimeout(() => {
    
    reject(3);
  }, 1000);
});

Promise.allSettled([pro, Promise.resolve(1), Promise.reject(2)]).then(
  (data) => {
    
    console.log(data);
  }
);

Promise.myAllSettled([pro, Promise.resolve(1), Promise.reject(2)]).then(
  (data) => {
    
    console.log(data);
  }
);