Builder模式ES6 nodejs

Question

当我尝试调用任何构建器“setter”方法时，我一直遇到麻烦

这是我的代码，User.js：

class User {

constructor(userBuilder) {
    this.email      = userBuilder.email;
    this.name       = userBuilder.name;
    this.surname    = userBuilder.surname;
    this.photo      = userBuilder.photo;
    this.tokens     = userBuilder.tokens;
    this.authorized = userBuilder.authorized;
}

getEmail() {
    return this.email;
}

getName() {
    return this.name;
}

getSurname() {
    return this.surname;
}

getPhoto() {
    return this.photo;
}

getTokens() {
    return this.tokens;
}

isAuthorized() {
    return authorized;
}

static get UserBuilder() {
    class UserBuilder {

        constructor() {
            this.email = null;
            this.name = null;
            this.surname = null;
            this.photo = null;
            this.tokens = null;
            this.authorized = null;
        }

        email(email) {
            this.email = email;
            return this;
        }

        name(name) {
            this.name = name;
            return this;
        }

        surname(surname) {
            this.surname = surname;
            return this;
        }

        photo(photo) {
            this.photo = photo;
            return this;
        }

        tokens(tokens) {
            this.tokens = tokens;
            return this;
        }

        authorized(authorized) {
            this.authorized = authorized;
            return this;
        }

        build() {
            return new User(this);
        }
    }

    return UserBuilder;
}

}
module.exports = User

我的UserTest.spec.js：

process.env.NODE_ENV = 'test'

//Import User class
let User = require('../../../../main/com/auth/user/User');

// Import chai
let chai = require('chai');

// Tell chai that we'll be using the "should" style assertions.
chai.should();

describe('User', () => {
let user;

var email       = "a@a";
var name        = "a";
var surname     = "a";
var photo       = "p";
var authorized  = true;

beforeEach(() => {
    //Create new User object before each test
    user = new User.UserBuilder()
        .email(email)
        .name(name)
        .surname(surname)
        .photo(photo)
        .authorized(authorized)
        .build();
});

it('returns the email', () => {
    user.getEmail().should.equal(email)
});

it('returns the name', () => {
    user.getName().should.equal(name)
});

it('returns the surname', () => {
    user.getSurname().should.equal(surname)
});

it('returns the photo', () => {
    user.getPhoto().should.equal(photo)
});

it('returns the authorized', () => {
    user.getAuthorized().should.equal(authorized)
});
})

我得到TypeError：user.email不是函数。

我尝试过用户类以外的UserBuilder：

在User.js中

module.exports = {User: User, UserBuilder: UserBuilder}

在UserTest.spec.js

中

let {User} = require('../../../../main/com/auth/user/User');
let {UserBuilder} = require('../../../../main/com/auth/user/User');

 user = new UserBuilder()
        .email(email)
        .name(name)
        .surname(surname)
        .photo(photo)
        .authorized(authorized)
        .build();

结果相同，我做错了什么？我可以调用build方法，但我不能调用任何其他方法。