Stopping execution flow after an error in express-validator
req.onValidationError(function(msg) {
    res.render('signup', { error: msg });
});

req.check('email', 'Please enter a valid email.').len(1,256).isEmail;
req.check('password', 'Your password must be at least 8 characters.').len(8,256);

var user = {
    email: req.body.email,
    password: req.body.password
};

User.create(user, function(err, result) {
    console.log(err, result);
});

res.render('signup');

var errors = [];
req.onValidationError(function(msg) {
    //res.render('signup', { error: msg });
    errors.push(msg);
});

req.check('email', 'Please enter a valid email.').len(1,256).isEmail;
req.check('password', 'Your password must be at least 8 characters.').len(8,256);

if (errors.length) return res.render('signup', { error: errors.join('n') });

var user = {
    email: req.body.email,
    password: req.body.password
};

User.create(user, function(err, result) {
    console.log(err, result);
});

res.render('signup');