Check if user already exist and wait for callback - node.js

Question

I have a small function to validate the user input. In that function I will also check if the email address is already taken. But I have some trouble with the async callback.
I hope anyone could give me a hint, how I could solve this. I use nodejs with the express 3 framework, mongodb and the node-validator library.
This is a part of my validation function:
function check(data, callback) {
mongoose.model('User', User).count(data, function (err, count) {
callback(err, !! count);
});
};
function validate(email, password, confirm) {
var v = new Validator(),
errors = new Array();
v.error = function (msg) {
errors.push(msg);
};
check({email: email}, function (err, exists) {
v.check(exists, { email: 'E-Mail is already taken' }).equals(false);
});
...
return errors;
}
Based on the async callback the variable errors is at the return statement empty. How could I else check if the email address is already in the databse?

Answer 1

You are going to have to add a callback to your validate function. As it stands now, your check function is asynch so you are immediately returning the empty errors array.
function check(data, callback) {
mongoose.model('User', User).count(data, function (err, count) {
callback(err, !! count);
});
};
function validate(email, password, confirm, callback) {
var v = new Validator(),
errors = new Array();
v.error = function (msg) {
errors.push(msg);
};
check({email: email}, function (err, exists) {
if (err) {
return callback(err);
}
v.check(exists, { email: 'E-Mail is already taken' }).equals(false);
callback(null, v);
});
};
// Calling to validate example
server.get("/validate_user_or_whatever", function(req, resp) {
// Call validate with callback
validate(req.param("email"), req.param("password"), true, function(err, validator) {
if (err) {
return resp.json({success: false, message: err.message});
}
var success = validator.isValid; // or something
// Respond with the results
resp.json({success: success});
});
});
Now, your next question is probably going to be how do I run all these validate functions and wait for them to return before calling the validate callback. Good question, take a look at the async module.

Answer 2

You need to think async and pass callbacks that will be called asynchronously.
Quick example:
app.get('/blah', function(req, res) {
// Whatever
validate(email, pass, confirm, function(errors) {
if (errors.length == 0)
resp.send(200, 'blah');
else
resp.send(400, 'blah blah');
});
})
function validate(email, password, confirm, callback) {
var v = new Validator(),
errors = new Array();
v.error = function (msg) {
errors.push(msg);
};
check({email: email}, function (err, exists) {
v.check(exists, { email: 'E-Mail is already taken' }).equals(false);
}, function() {
callback(errors);
});
// ...
return errors;
}