Can't push data from firebase to array by using foreach in Node.js

Question

I tried to fetch data from firebase firestore, which I get what I wanted by console.log(). But when I tried to store what I get to array using push(). It gives me empty value in return. Here is my code:

app.post('/getMemberInfo', async (req, res) => {
  var memberKeyList = req.body.member
  var memRef = await db.collection("user")
  let newArray = []
  memberKeyList.forEach((row) => {
    memRef.doc(row.MemberID).get().then((doc)=>{

        newArray.push(doc.data())
        console.log(doc.data())

      

    })
    
  })
  res.send(newArray)
})

Here on console.log I got all data, but in newArray it returns empty array. What did I do wrong here? Any solution?

Frank van Puffelen · Accepted Answer · 2022-07-20 17:20:36Z

1

The problem is that each get() call is an asynchronous operation, and your res.send(newArray) runs before any of these calls complete (which you can see by adding some more logging and checking the order of the output).

The solution is to use Promise.all to wait for all the asynchronous operations to complete before sending the result back to the client:

app.post('/getMemberInfo', async (req, res) => {
  var memberKeyList = req.body.member
  var memRef = await db.collection("user")
  let newArray = []
  const docs = Promise.all(memberKeyList.map((row) => memRef.doc(row.MemberID).get()));
  const newArray = docs.map((doc)=> doc.data());
  res.send(newArray)
})

answered Jul 20, 2022 at 17:20

Frank van Puffelen

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1 Comment

Jack Venevankham Over a year ago

I got empty on docs, it doesn't give any result.

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