Firebase中的异步功能甚至在功能主体完成执行之前就解决了承诺

如何解决Firebase中的异步功能甚至在功能主体完成执行之前就解决了承诺

因此，我有一个异步函数，该函数将自定义对象的数组作为参数，然后遍历每个对象并从Firestore获取一些数据。 Firestore中的数据将转换为另一个自定义对象，并添加到另一个自定义对象数组中。这些对象的长度由函数返回。

async function getCompsReceived(theInterestedPeople: InterestedPerson[]) {

  const whatsNewObjects: WhatsNewObject[] = []

  theInterestedPeople.forEach(async (person) => {

    const documentsSnapshot = await 
    db.collection('Users').doc(person.uid).collection('complimentsReceived')
      .orderBy('receivedTime','desc')
      .limit(documentLimit)
      .get()

  if (documentsSnapshot.empty) {
    console.log(`${person.userName} has no compsReceived`)
    return
  }


  await documentsSnapshot.forEach((newCompReceived: { receiverUid: string; receiverUserName: string; 
    complimentsReceivedContent: string | null; hasImage: boolean | null; senderUid: string | null; 
      senderUserName: string | null; noOfLikes: number | null; receivedTime: number | null; 
        complimentId: string | null} ) => {
         //Add each new Compliment to the WhatsNewObjects Array
         const whatsNewDoc = new WhatsNewObject(
           newCompReceived.receiverUid,newCompReceived.receiverUserName,true,newCompReceived.complimentsReceivedContent,newCompReceived.hasImage,newCompReceived.senderUid,newCompReceived.senderUserName,newCompReceived.noOfLikes,newCompReceived.receivedTime,newCompReceived.complimentId,'PERSON_COMPLIMENT_RECEIVED'
         )

    whatsNewObjects.push(whatsNewDoc)

  })

  console.log(`length of whatsNewObjects after adding ${person.userName}'s compsReceived is      
    ${whatsNewObjects.length}`)

})

console.log(`returning the length of WhatsNewObjects at getCompsReceived which is ${whatsNewObjects.length}}`)
    return whatsNewObjects.length

}

问题在于此函数始终返回0，并且在Firebase控制台上打印了日志语句，我看到该函数的主体在该函数已经返回了一个值为Promise的值之后正在执行。

有人可以帮助我如何使函数在返回whatsNewObjects.length之前等待主体执行吗？

解决方法

您不应使用forEach来迭代异步代码，因为它不会await。它将一劳永逸。改为使用for..of：

async function getCompsReceived(theInterestedPeople: InterestedPerson[]) {

    const whatsNewObjects: WhatsNewObject[] = []

    for (const person of theInterestedPeople) {
        const documentsSnapshot = await db.collection('Users').doc(person.uid).collection('complimentsReceived')
            .orderBy('receivedTime','desc')
            .limit(documentLimit)
            .get();

        if (documentsSnapshot.empty) {
            console.log(`${person.userName} has no compsReceived`)
            return;
        }

        documentsSnapshot.forEach((newCompReceived: {
            receiverUid: string; receiverUserName: string;
            complimentsReceivedContent: string | null; hasImage: boolean | null; senderUid: string | null;
            senderUserName: string | null; noOfLikes: number | null; receivedTime: number | null;
            complimentId: string | null
        }) => {
            //Add each new Compliment to the WhatsNewObjects Array
            const whatsNewDoc = new WhatsNewObject(
                newCompReceived.receiverUid,newCompReceived.receiverUserName,true,newCompReceived.complimentsReceivedContent,newCompReceived.hasImage,newCompReceived.senderUid,newCompReceived.senderUserName,newCompReceived.noOfLikes,newCompReceived.receivedTime,newCompReceived.complimentId,'PERSON_COMPLIMENT_RECEIVED'
            );
            whatsNewObjects.push(whatsNewDoc);

        })
        console.log(`length of whatsNewObjects after adding ${person.userName}'s compsReceived is ${whatsNewObjects.length}`);
    }
    console.log(`returning the length of WhatsNewObjects at getCompsReceived which is ${whatsNewObjects.length}}`);
    return whatsNewObjects.length;
}

,

问题与forEach有关，即使您在回调函数中使用async/await，它实际上也会异步运行。 您只需将forEach更改为任何类型的for迭代器即可解决此问题。

for (let index = 0; index < theInterestedPeople.length; index++) {
    const person = array[index];
    ....your code
}
// or
for (const person of theInterestedPeople) {
    
}
// or