如何从 Array.reduce 返回 Return Promise答案

【问题标题】：How to return Return Promise from Array.reduce如何从 Array.reduce 返回 Return Promise
【发布时间】：2022-11-07 22:06:33
【问题描述】：

我正在使用Array.reduce 迭代一组对象并尝试从那里返回承诺。我在 reduce 方法中进行了一些修改，并且在对象中的 promise 解析后 reviewCards['departments'] 键具有修改后的数据，但 reviewCards['genders'] 为空。我认为所有的承诺都没有正确解决。

如何将最终对象作为 Promise 返回？

public getCompanyReviewCards(
   reviewGroups: ICompanyReviewGroups,
   reviews: CompanyReview[],
): Promise<[key: string]: ICompanyReviewCard> {
  
   return new Promise((resolve, reject) => { 
      const reviewCards = Object.keys(reviewGroups).reduce(
         async (reviewCards: ICompanyReviewCards, groupKey: string) => {

            const group = reviewGroups[groupKey];
            reviewCards['genders'] = reviewCards['genders'] || [];
            reviewCards['departments'] = reviewCards['departments'] || [];

            //Department wise cards
            //This block is excuting properyly
            if (groupKey === '_departmentGroup') {
                 const departmentsCards = await this.getCardsByDepartments(group);
                 reviewCards['departments'] = departmentsCards;
            }

            //Gender wise cards
            //This block is not excuting properyly
            if (groupKey === '_genderGroup') {
                 const gendersCards = await this.getCardsByGender(group);
                 reviewCards['genders'] = gendersCards;
            }

            return reviewCards;

         },Object.create(null),
      );

   resolve(reviewCards);

   })
}

【问题讨论】：

标签： javascript types promise

【解决方案1】：

如果你返回一个承诺，你也必须等待它：`await reviewCards"

【讨论】：

我需要在哪里使用await，你能解释一下吗？

【解决方案2】：

reduce 不知道承诺，也不会自动处理你的承诺，所以你必须自己做。请记住，回调的第一个参数是从上一次迭代返回的值，这将是一个承诺。

const main = async() => {
  const generateNumber = () => {
    return new Promise(resolve => setTimeout(() => resolve(Math.random()), 1000));
  };

  const data = ['a', 'b', 'c'];
  const promiseReducedData = data.reduce(async(previousValuePromise, currentValue, index) => {
    const resolvedPreviousValue = await previousValuePromise;
    console.log(`Working on index ${index}`);
    const newValue = {
      ...resolvedPreviousValue,
      [currentValue]: await generateNumber()
    };
    return newValue;
  }, {});
  const reducedData = await promiseReducedData;
  console.log(reducedData);
};

main();

【讨论】：