手写原理 | Promise.allSelected

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Promise.allSettled()方法返回一个在所有给定的 promise 都已经fulfilled或rejected后的 promise，并带有一个对象数组，每个对象表示对应的 promise 结果

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

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function myPromiseAllSelected(promises) {
    return new Promise((resolve, reject) => {
        let res = [];
        let iteratorIndex = 0;
        let fullCount = 0;
        
        for (let item of promises) {
          let resIndex =  iteratorIndex;
          iteratorIndex++;
            
          Promise.resolve(item).then(value => {
              res[resIndex] = {
                  status: 'fulfilled',
                  value,
              };
              fullCount++;
              
              if (fullCount === iteratorIndex) {
                  resolve(res);
              }
          }).catch(reason => {
              res[resIndex] = {
                  status: 'rejected',
                  reason,
              };
              fullCount++;
              
              if (fullCount === iteratorIndex) {
                  resolve(res);
              }
          })
        };
    })
};


// test

let p1 = Promise.resolve(3);
let p2 = Promise.reject(2);

Promise.allSettled([p1, p2]).then(val => {
    console.log(val)
}). catch(err => {
    console.log(err)
});  

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


myPromiseAllSelected([p1,p2]).then(res => console.log(res), err => console.log(err))