Typescript and Immutable.js Record usage example.

index.ts

import * as Immutable from 'immutable';

const UserRecord = Immutable.Record({
    id: '',
    age: 0
}, 'User');

class User extends UserRecord {
    public readonly id: string;
    public readonly age: number;

    constructor(
        id: string,
        age: number
    ) {
        super({ id, age });
    }

    updateId(f: (id: string) => string): User {
        return <User>this.update('id', f);
    }
    updateAge(f: (age: number) => number): User {
        return <User>this.update('age', f);
    }
}

const john = new User('USER:JOHN', 18);

console.log(john);

// Emits error `Left-hand side of assignment expression cannot be a constant or a read-only property.`
// john.age = 21;

console.log(john);

const bob = john.updateId(() => 'USER:BOB').updateAge(() => 21);

console.log(john.id, bob.id);

const list = Immutable.List([john, bob]);

list.forEach(user => { console.log(user.age) })