mongoose express计数器不递增,范围问题

返回的计数器值始终为0。为什么?我怎样才能解决这个问题? 在messages.findOne中有正确的计数器值。在conversation.forEach中,计数器值始终为空。

router.get('/isNewMessages', auth, async(req, res) => {
    try{
        const query={usernames: req.user.username}
        Conversation.find(query, (err, conversations)=>{
            var counterNewMessages = 0
            conversations.forEach(conversation=>{
                    console.log(counterNewMessages) // Here is always 0
                    Messages.findOne({_id:conversation.messages},(err,messages)=>{
                        counterNewMessages +=  messages.messages.filter(message=>!message.isRead && message.receiver === req.user.username).length
                        console.log(counterNewMessages) // Here is value is correct
                     })
            })
            res.status(201).send({counterNewMessages})
        })
    }catch(e){
        res.status(400).send(e)
    }
})

解决方案(在接受的答案中解释):

router.get('/isNewMessages', auth, async(req, res) => {
    try{
        const query={usernames: req.user.username}
        Conversation.find(query,  async (err, conversations)=>{
            let counterNewMessages = 0
            for(const conversation of conversations){
                await Messages.findOne({_id:conversation.messages},(err,messages)=>{
                    counterNewMessages +=  messages.messages.filter(message=>!message.isRead && message.receiver === req.user.username).length
                 })
            }
            res.status(201).send({counterNewMessages})
        })
    }catch(e){
        res.status(400).send(e)
    }
})