Example of using Incapsulation + Abstraction + Interface Contract

person.ts

interface BasePerson {
  firstName: string;
  lastName: string;
  password: string;
  apiToken: string;
}

interface ShowProfile {
  showProfile(): string;
}

class Person implements BasePerson {
  #firstName: string;
  #lastName: string;
  #password: string;
  #apiToken: string;

  constructor(
    firstName: string,
    lastName: string,
    password: string,
    apiToken: string,
  ) {
    this.#firstName = firstName;
    this.#lastName = lastName;
    this.#password = password;
    this.#apiToken = apiToken;
  }

  get firstName(): string {
    return this.#firstName;
  }

  get lastName(): string {
    return this.#lastName;
  }

  get password(): string {
    return this.#password;
  }

  get apiToken(): string {
    return this.#apiToken;
  }
}

class SecurePerson implements BasePerson {
  private person: Person;

  constructor(person: Person) {
    this.person = person;
  }

  get firstName(): string {
    return this.person.firstName;
  }

  get lastName(): string {
    return this.person.lastName;
  }

  get password(): string {
    return "********";
  }

  get apiToken(): string {
    return "********" + this.person.apiToken.slice(-3);
  }
}

class PersonProfile implements ShowProfile {
  private person: BasePerson;

  constructor(person: BasePerson) {
    this.person = person;
  }

  showProfile(): string {
    return `First name: ${this.person.firstName}
Last name: ${this.person.lastName}
Password: ${this.person.password}
API Token: ${this.person.apiToken}`;
  }
}

interface Greeter {
  greet(person: BasePerson): string;
}

class OfficeGreeter implements Greeter {
  greet(person: BasePerson): string {
    return `${person.firstName} ${person.lastName} welcome to the office!`;
  }
}

const person = new Person(
  "John",
  "Doe",
  "qwerty",
  "uvb4f-4f4f-4f4f-4001",
);
const personProfile = new PersonProfile(person);
console.log(personProfile.showProfile());

const securePerson = new SecurePerson(person);
const securePersonProfile = new PersonProfile(securePerson);
console.log(securePersonProfile.showProfile());

const officeGreeter = new OfficeGreeter();
console.log(officeGreeter.greet(person));
console.log(officeGreeter.greet(securePerson));
officeGreeter.greet = (person: BasePerson) => {
  // evil code
  return `Hijack ${person.firstName} ${person.lastName} private data ${person.password} ${person.apiToken}`;
};
console.log(officeGreeter.greet(person));
console.log(officeGreeter.greet(securePerson));