mongodb query with javascript, cursor methods

I am just creating a simple user login for using MongoDB, Backbone and Node with Express.

I am stuck on querying the database for the user credentials and reliably identifying whether they exist or not.

I'm trying two things here:

// When user posts to the url
app.post('/save/user', function (req, res) {

  // create user object and store email from form
  var user = {
    email : req.body.email
  };

  // in my collection users
  db.collection('users', function (err, collection) {

    // create a variable existence with the value, in lamens terms 'yes it does' or 'no it doesnt'
    var existence = findOne(collection, {
      $query : {email : user.email}
    });

  });
};

// findOne function passing the collection and the query object
function findOne(coll, query) {
  var cursor = coll.find(query).limit(1);
  return cursor.hasNext() ? cursor.next() : null;
}

So this is the first way I've been trying. Thing is, I don't understand why the cursor doesn't have 'next(), hasNext(), findOne(), forEach()' and other methods for javascript environment but only for mongo shell.

My question is, how do I access these methods from in my Node.js app?

The second way I tried it :

// When user posts to the url app.post('/save/user', function (req, res) {

  // create user object and store email from form
  var user = {
    email : req.body.email
  };

  // in my collection users
  db.collection('users', function (err, collection) {

    // Have a look for the email entered
    var query = collection.find({
      $query : {email : user.email}
    }).limit(1);

    // If it's true, then send response
    query.each( function (err, item) {

      // If the item does exists, then send back message and don't insert. Otherwise, insert.
      if(item !== null) {
        console.log('Item does not equal null : ', item);
        res.send('The email : ' + item.email + ' already exists');
      } else {
        console.log('Item does equal null : ', item);
        collection.insert(user);
        res.send('New user with email : ' + user.email + ' was saved');
      }

    });

  });
};

The problem with this is, it's always going to return null at some point and so I am going to warn the user 'it already exists' and then the next time will be null so it's going to save the email.

I think i'm missing the point so a point in the right direction would be great.

Many thanks in advance!

Well i've looked into a solution but still must be missing the point.

I'm doing an insert, passing in my user object with safe : true but although multiple user objects can be entered, it's still only looking for identical ID;s. I've tried creating an id with new ObjectID() but I still don't understand if a user enters their email adress, thenattempts to create a new user with the same email, it would create a new id for that entry.

By doing the findOne, I can see if it exists easily, Idon't see how it can be done with insert.

app.post('/register/user', function (req, res) {

// Store user details in object
var user = {
  username : req.body.user,
  email : req.body.email,
  password : req.body.password
};

db.collection('users', function (err, collection) {

  collection.insert(user, {safe : true}, function (err, doc) {

    console.log('what is doc : ', doc);
    if(!err) {
      res.writeHead(200, {
        "Content-Type" : "text/plain",
        "Message" : "New user added",
        "Access-Control-Allow-Origin" : "*"
      });
    } else {
      console.log('Error is : ', err);
      res.writeHead(200, {
        "Content-Type" : "text/plain",
        "Message" : "User already exists",
        "Access-Control-Allow-Origin" : "*"
      });
    }

    res.end();

  });

});

});