我有一个这样的对象数组:

聚合结果给我一个结构相同的结果如下:

results = [
  {id: 1, test: biology, candidates:[ {cid: 11},{cid: 12},{cid: 13}]},
  {id: 2, test: chemistry, candidates:[ {cid: 15},{cid: 16},{cid: 17}]},
  {id: 3, test: physics, candidates:[ {cid: 1},{cid: 6},{cid: 7}]}
];

所以我需要在数组中循环，然后为每个候选人调用一个 promise 函数 getTotalMarksPerCandidate(它有一个 Promise.all 并在一些计算后解析变量)。但是，由于在数组中循环，不等待 promise 完成，我得到了 promise...

问题:你知道我怎样才能解决这个问题，以便在我的候选人数组中循环时，它会等待结果并继续吗？或任何周转解决方案？

所以我映射到结果数组，然后在候选数组中执行 forEach，以候选对象作为参数调用函数 getTotalMarksPerCandidate，将结果推送到 promise 数组中。然后将解决收到的所有 promise 。

var new_Result = results.map( function (subject) {
 let promises = [];
 if (subject.candidates && subject.candidates.length > 0) {
  subject.candidates.forEach( (element) => {
   promises.push(mobileUtil. getTotalMarksPerCandidate(element));
  });
 }
 return Promise.all(promises).then( result => {
  console.log('Check this out', result);
  subject.newCandidatelist = result;
  return subject;
 });
});
console.log('R: ', new_Result);
resolve(params);

所以在 return Promise.all(promises) 回调函数中，我可以看到 promises 正在被解析，并且我看到函数 getTotalMarksPerCandidate 的返回值。我怎样才能将带有 totalMarks 的新候选对象设置为它们各自的父对象，如

new_results = [
{id: 1, test: biology, candidates:[ {cid: 11, score: 88},{cid: 12, score: 90},
  {cid: 13, score: 91}]},
{id: 2, test: chemistry, candidates:[ {cid: 15, score: 91},{cid: 16, score: 91}, 
  {cid: 17, score: 91}]},
{id: 3, test: physics, candidates:[ {cid: 1, score: 91},{cid: 6, score: 91},
  {cid: 7, score: 91}]}
];

谢谢

最佳答案

一种完全基于嵌套 Promise 链的方法如下:

/*
Obtain array of promises via results.map() and resolve each sequentially
*/
const new_Result = Promise.all(results.map((subject) => {

    /* 
    Start a promise chain for this subject 
    */
    return Promise.resolve()
    .then(() => {

        /* 
        Get candidates from current subject, or just an empty array if no valid candidates data present 
        */
        const candidates = Array.isArray(subject.candidates) && subject.candidates.length > 0 ? subject.candidates : [];

        /*
        Map candidates (if any) to this Promise.all() 
        */
        return Promise.all(candidates.map((candidate) => {
            return mobileUtil.getTotalMarksPerCandidate(element).then(function(score) {
                /*
                Assign the score returned from getTotalMarksPerCandidate() for current candidate object
                */
                candidate.score = score;

                /*
                Return the updated candidate to mapped array of promise results
                */
                return candidate;
            })
        }));
    })
    .then((result) => {

        console.log('Check this out', result);
        subject.newCandidatelist = result;
        return subject;
    });
}));

这里的关键添加是这些行，它们基本上将从 getTotalMarksPerCandidate() 的已解决 promise 返回的分数值“附加”到正在迭代的当前 candidate:

return mobileUtil.getTotalMarksPerCandidate(element).then(function(score) {

    candidate.score = score;

    return candidate;
})

希望对您有所帮助!

关于javascript - 如何处理嵌套循环中的 promise ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/57566670/