How to sort my array of objects based on firebase Timestamp

Question

I need my messages should be ordered based on timestamp ("createdAt" is the name of filed) i can do it in earlier versions of firebase but cant fig out how to do it in firebase v9

DATA STRUCTURE ON FIRESTORE

SEE IMAGE HERE

const [messages, setMessages] = useState([])
    useEffect(() => {

        const unsub = onSnapshot(doc(db, "messages", state.id), (snapshot) => {
            if(snapshot.data()){
                console.log(123,Object.values(snapshot.data()))
                setMessages(Object.values(snapshot.data()))
            }
        });
    }, [])

Frank van Puffelen · Accepted Answer · 2022-03-26 14:23:30Z

2

What you have in your document is not an array. They are just fields with random IDs. You can sort them using .sort() as shown below:

if (snapshot.data()) {
  const sortedMessages = Object.values(snapshot.data()).sort((a, b) => a.createdAt.toMillis() - b.createdAt.toMillis())

  setMessages(sortedMessages);
}

edited Mar 26, 2022 at 14:23

Frank van Puffelen

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answered Mar 26, 2022 at 12:59

Dharmaraj

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6 Comments

Arnab Kumar Over a year ago

This is working and doing the job but its crashes after each msg is sent ERROR : TypeError: Cannot read properties of null (reading 'toMillis')

Dharmaraj Over a year ago

@ArnabKumar that means createdAt field is missing from the document. Are you sure that field is present ? Also just .sort((a, b) => a.createdAt - b.createdAt) should do it iirc.

Arnab Kumar Over a year ago

Yes 100% sure it is present

Dharmaraj Over a year ago

@ArnabKumar can you console.log(snapshot.data()) before this sort function and share the output to ensure that?

Arnab Kumar Over a year ago

its working after removing the .toMilis()

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