Simple example for email Address value object

email-address.js

var address;

var setAddress = function(address) {
    /**
     * @todo add validation here
     */
    address = address;
};

function EmailAddress(anAddress) {
    setAddress(address);
    Object.defineProperty(this, 'address', {
        value: () => { return address; }
    });
    Object.freeze(this);
}

EmailAddress.prototype = {
    equals(other) {
        return this === other;
    },
    toString(){
        return this.address();
    },
    valueOf() {
        return this.address();
    }
};

EmailAddress.fromString = function(anAddress) {
    return new EmailAddress(anAddress);
};

email-address.spec.js

let expect = require('chai').expect;
let EmailAddress = require('../../../../src/domain/model/passenger/email-address');

describe('Email value object', () => {
    describe('Immutability', () => {
        beforeEach(() => {
            this.emailAddress = new EmailAddress('cherif@site.com');
        });
       
        it('must be frozen', () => {
            expect(Object.isFrozen(this.emailAddress)).to.be.true;
        });

        it('is not enumerable', () => {
            expect(this.emailAddress.hasOwnProperty('email')).to.be.false;
        });
    });
});