Node.js mongoose query if item exist in array,and insert and update if does not...

nodequery.js

exports.user_post_emails = function(req, res){
  
	var emails 	= [];
		
	Mongoose_Collection.findOne({userId: req.user._id}, function(err, user){
		if(!user){
			emails[0] = req.body.emails;
			new Mongoose_Collection({
				emails: emails,
				userId:req.user._id
			}).save();		
		} else {
			// the current length of the array..
			Mongoose_Collection.findOne({userId: req.user._id}, function(err, user){
				_length = user.emails.length;
				function in_array(array, id) {
				    for(var i=0;i<array.length;i++) {
				        if(array[i][0].id === id) {
				            return true;
				        }
				    }
				    return false;
				}

				var result = in_array(user.emails, req.body.emails);

				if(!result){
					emails = user.emails;
					emails[_length] = req.body.emails;
					Mongoose_Collection.update({
						userId: req.user._id
					}, {
						$set: {
							emails: emails
						}
					}).exec();
				}

			});
		}
	})

	res.render("user", {
		username: req.user.username,
		user: req.user
	})
}