await 仅在 nodejs 中的异步 function 中有效

Question

I have a built an app with flutter + firebase, I need to delete document if it was create more than 5 hours ago so I built a script with nodejs. The problem is that documents are not deleted because I don't wait the delete function to finsh. So I tried to add async/await but I have an error.

I tried to do this:

async function mydelete(){
let getDoc = cityRef.get()
    .then(snapshot => {
        snapshot.forEach(doc => {
            docid = doc.id;
            if (doc.id.length == 4)
                db.collection('collection').doc(doc.id).delete();
            else if (doc.data().Timestamp._seconds < new Date() - 18000) {
                console.log(doc.id)
                a = await db.collection('collection').doc(doc.id).delete()
            }
            else console.log('false')
        })
    })
    .catch(err => {
        console.log('Error getting documents', err);
    });

}

But now I have this error: SyntaxError: await is only valid in async function

Answer 1

You can not use await without async keyword in any function including callback function also. So snapshot.forEach(doc => {...}) should be: snapshot.forEach(async doc => {...})

error: SyntaxError: await is only valid in an async function

To be able to use await inside the function the syntax always must be like below

 async function () {

    await  functionReturnsPromise()      
  }

The below code is wrong you will get above error:

 async function () {   
          functionTest(()=>{
           await  functionReturnsPromise()  
        })

   }

We will have to put async keyword before the callback function to be able to run the code as below

  async function () {

              functionTest( async ()=>{
               await  functionReturnsPromise()  
            })

Change your code something like below:

async function mydelete() {
        try {
            let snapshot = await cityRef.get() 
            snapshot.forEach(async (doc) => {

               let docid = doc.id;

              if (doc.id.length == 4)
                    await db.collection('collection').doc(doc.id).delete();

               else if (doc.data().Timestamp._seconds < new Date() - 18000) {
                     console.log(doc.id)
                    let a = await db.collection('collection').doc(doc.id).delete()
                } else console.log('false')
            })
        }

  catch (err) {
     // handle error here 
  }
} 

Note: there might be a syntax error in code in the above code