Node Js - SyntaxError: await 仅在异步函数中有效

Question

我在 service.js 文件中有以下代码。

exports.getSeminarDetailsById = async function (seminarId) {
try {
    let SeminarList = [];
    var seminarData = await SeminarRepository.getSeminarDetailsById(seminarId);
    if (seminarData && seminarData.length > 0) {
        let userIdList = [...new Set(seminarData.map(x => x.user_id))];
        if (userIdList && userIdList.length > 0) {
            let userDetails = await EmployeeRepository.getEmployeeDetailsByUserIds(userIdList);
            if (userDetails && userDetails.length > 0) {
                seminarData.forEach(element => {
                    let seminarDetail;
                    let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
                    let categoryName;
                    if (element.category_id == 1)
                        categoryName = AppConstants.seminarCategoryName.TECHNICAL;
                    else
                        categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;

                    seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
                    await mapAttachmentWithSeminar(seminarId, seminarDetail);
                    console.log("second", seminarDetail);
                    SeminarList.push(seminarDetail);
                });
            }
        }
    }
    return SeminarList;
} catch (err) {
    console.log(err);
    throw err;
}
}

await mapAttachmentWithSeminar(seminarId, seminarDetail); 出现此错误，它在以下同一文件中定义。

async function mapAttachmentWithSeminar(seminarId, seminarDetail) {
var seminarAttachmentDetails = await SeminarRepository.getSeminarAttachmentDetailsById(seminarId);
  if (seminarAttachmentDetails && seminarAttachmentDetails.length > 0) {
    let AttachmentDetails = [];
    seminarAttachmentDetails.forEach(element => {
        let attachmentDetails = new SeminarAttachmentDetails(element);
        AttachmentDetails.push(attachmentDetails);
    });
    seminarDetail.SeminarAttachmentDetails = AttachmentDetails;
  }
  else {
    seminarDetail.SeminarAttachmentDetails = null;
    console.log("first", seminarDetail);
  }
}

如果我删除 await 函数，那么在执行函数 mapAttachmentWithSeminar() 之前将首先执行 console.log("second", seminarDetail);。这样从该函数返回的SeminarAttachmentDetails 的值将被遗漏，如下所示：

这是预期的输出。

Answer 1

您可以使用经典的for 循环而不是使用.forEach

for(let i = 0; i < seminarData.length; i++){
    let element = seminarData[i];
    let seminarDetail;
    let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
    let categoryName;
    if (element.category_id == 1)
        categoryName = AppConstants.seminarCategoryName.TECHNICAL;
    else
        categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;

    seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
    await mapAttachmentWithSeminar(seminarId, seminarDetail);
    console.log("second", seminarDetail);
    SeminarList.push(seminarDetail);
}

Answer 2

首先，您使用了错误的异步等待。您在非异步函数的范围内等待。 这里：

 seminarData.forEach(element => {
                let seminarDetail;
                let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
                let categoryName;
                if (element.category_id == 1)
                    categoryName = AppConstants.seminarCategoryName.TECHNICAL;
                else
                    categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;

                seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
                await mapAttachmentWithSeminar(seminarId, seminarDetail);
                console.log("second", seminarDetail);
                SeminarList.push(seminarDetail);
            });

你应该有这个

 // here you have the SeminarList but promisified
 // with the form Promise<SeminarListItem>[]
 // to get the values out of the promises you have to await this array     
    const promisifiedSeminarList = seminarData.map((element)=>{
         let userName = userDetails.filter(x => x.user_id == element.user_id).map(
            x => x.userfullname)[0]
         );

        const categoryName = elemenet.category_id == 1
          ? AppConstants.seminarCategoryName.TECHNICAL
          : AppConstants.seminarCategoryName.NONTTECHNICAL;

       const seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
       return mapAttachmentWithSeminar(seminarId, seminarDetail);
    });
  // now
   const seminarList = await Promise.all(promisifiedSeminarList);

为此，您需要函数 mapAttachmentWithSemniar 返回一个未发生的值

Answer 3

每个嵌套函数都应该声明为async 以及父函数。 在您的情况下，此声明在嵌套级别之一中丢失，请注意这部分代码

seminarData.forEach(async element => {
//                  ^^^^ async missed here
 let seminarDetail;
 let userName = userDetails.filter(x => x.user_id == element.user_id).map(x => x.userfullname)[0];
 let categoryName;
 if (element.category_id == 1)
  categoryName = AppConstants.seminarCategoryName.TECHNICAL;
 else
  categoryName = AppConstants.seminarCategoryName.NONTECHNICAL;
 seminarDetail = new SeminarTrackerDetails(element, userName, categoryName);
 await mapAttachmentWithSeminar(seminarId, seminarDetail); 
 console.log("second", seminarDetail); 
 SeminarList.push(seminarDetail);
});