I am trying to perform a sign up form into Mongo Node.js and Express.js. I have already completed the task which inserts a document into users collection for a new user. But I need to create a validation if a user exist based on username or email as keys.

For example I am submitting a user: { "_id": { "$oid": "62ac54c4cd1c80d0e8e2f68a" }, "firstName": "test", "lastName": "test", "email": "test@test.com", "password": "test", "username": "test"}

If I try to sumbit the same creds in the sign up form, my API completely crashes with error code:

db.collection(...).exists is not a function

Note: I am using mongoose

Code:

app.post("/login", async (req, res) => {
    const firstName = req.body.firstName;
    const lastName = req.body.lastName;
    const email = req.body.email;
    const password = req.body.password;
    const username = req.body.username;

    var data = {
        "firstName": firstName,
        "lastName": lastName,
        "email": email,
        "password": password,
        "username": username
    }

    console.log(data);

    let userExist = await db.collection('users').exists({ "username": username, "email": email })
    console.log(userExist);

    if (userExist) {
        console.log("User already exists");
        return res.render('login');
    } else {
        db.collection('users').insertOne(data, function (err, collection) {if (err) throw err;});
    }
    res.render('login', { 'data': data });
});

Any ideas?