immutable.ts

export class Immutable<S> {
  private obj: S;
  constructor(obj: S) {
    Object.freeze(obj);
    if (typeof obj === 'object') {
      Object.keys(obj).forEach((key: string): void => {
        Object.freeze(obj[key]);
      });
    }
    this.obj = obj;
  }

  get v(): S {
    return this.obj;
  }

  set(f: (objCopy: S) => S): Immutable<S> {
    let objCopy: S;
    if (Array.isArray(this.obj)) {
      objCopy = (<any>this.obj).slice();
    } else if (typeof this.obj === 'object') {
      objCopy = Object.assign({}, this.obj);
    } else {
      objCopy = this.obj;
    }
    return new Immutable(f(objCopy));
  }
}

nested.ts

import {Immutable} from './immutable';
import {Person} from './simple';

type GangMember = Immutable<Person>;
interface Gang {
  sign: string;
  assets: string[];
  members: Immutable<GangMember[]>;
}

let gang: Immutable<Gang>;
let member1 = new Immutable({ name: 'John', height: 1337 });
let member2 = new Immutable({ name: 'Doe', height: 42 })''
gang = new Immutable<Gang>({
  sign: 'frontend',
  assets: ['tags'],
  members: new Immutable([
    member1,
    member2
  ]),
});

let homer = new Immutable({ name: 'Homer', height: 110 });

console.log(gang.v.assets.length) // 1
try {
  gang.v.assets.push('attributes');
} catch (e) {
  // TypeError: Can't add property "attributes", object is not extensible
}
console.log(gang.v.assets.length) // 1

console.log(gang.v.members.v.length); // 2
gang = gang.set((gang: Gang): Gang => {
  gang.members = gang.members.set((members: GangMember[]): GangMember[] => {
    members.push(homer);
    return members;
  });
  return gang;
});
console.log(gang.v.members.v.length); // 3
console.log(gang.v.members.v[0] === member1); // true

console.log(gang.v.members.v[2].v.name); // Homer
homer.v.name = 'Bart';
console.log(gang.v.members.v[2].v.name); // Homer
gang = gang.set((gang: Gang): Gang => {
  gang.members = gang.members.set((members: GangMember[]): GangMember[] => {
    members.push(homer);
    members[2] = members[2].set((member: Person): Person => {
      member.name = 'Bart';
      return member;
    });
    return members;
  });
  return gang;
});
console.log(gang.v.members.v[2].v.name); // Bart

simple.ts

import {Immutable} from './immutable';

export interface Person {
  name: string;
  height: number;
}

let person: Immutable<Person>;
person = new Immutable({
  name: 'John',
  height: 1337,
});

console.log(person.v.name); // John
person.v.name = 'Doe';
console.log(person.v.name); // John

person = person.set((person: Person): Person => {
  person.name = 'Doe';
  return person;
});
console.log(person.v.name); // Doe