Throwing custom errors from Mongoose pre middleware and using Bluebird promises - node.js

Question

I am using Mongoose with Bluebird promises. I am trying to throw a custom error in a validate pre middleware and have it catchable with a Bluebird catch.
Here is my pre validate method
schema.pre('validate', function(next) {
var self = this;
if (self.isNew) {
if (self.isModified('email')) {
// Check if email address on new User is a duplicate
checkForDuplicate(self, next);
}
}
});
function checkForDuplicate(model, cb) {
User.where({email: model.email}).count(function(err, count) {
if (err) return cb(err);
// If one is found, throw an error
if (count > 0) {
return cb(new User.DuplicateEmailError());
}
cb();
});
}
User.DuplicateEmailError = function () {
this.name = 'DuplicateEmailError';
this.message = 'The email used on the new user already exists for another user';
}
User.DuplicateEmailError.prototype = Error.prototype;
I am calling the save with the following in my controller
User.massAssign(request.payload).saveAsync()
.then(function(user) {
debugger;
reply(user);
})
.catch(function(err) {
debugger;
reply(err);
});
This results in the .catch() having an error that looks like this:
err: OperationalError
cause: Error
isOperational: true
message: "The email used on the new user already exists for another user"
name: "DuplicateEmailError"
stack: undefined
__proto__: OperationalError
Is there a way for me to have the custom error be what is delivered to the catch? I want tis so I can check for the error type, and have the controller respond with the appropriate message back in the response.

Answer 1

User.DuplicateEmailError.prototype = Error.prototype;
is wrong, it should be
User.DuplicateEmailError.prototype = Object.create(Error.prototype);
User.DuplicateEmailError.prototype.constructor = User.DuplicateEmailError;
Or better use
var util = require("util");
...
util.inherits(User.DuplicateEmailError, Error);