Partial

partial.ts

interface Book {
    id: number;
    title: string;
    subject: 'crime' | 'comedy';
    body: string;
}

class BookRepository {
    constructor(private model: Book) {}
    update( model: Partial<Book> ) {
        // Update model
        this.model = Object.assign(this.model, model);
        console.log(this.model);
    }
}

let book: BookRepository = new BookRepository({
        id: 13,
        subject: 'crime',
        title: 'Arsène Lupin, Gentleman Burglar',
        body: 'Leblanc`s creation, gentleman thief Arsène Lupin, is everything you would expect from a French aristocrat - witty, charming, brilliant, sly ... and possibly the greatest thief in the world.'
    });


book.update({
    subject: 'comedy'
});

/**
 *  {
        "id": 13,
        "subject": "comedy",
        "title": "Arsène Lupin, Gentleman Burglar",
        "body": "Leblanc`s creation, gentleman thief Arsène Lupin, is everything you would expect from a French aristocrat - witty, charming, brilliant, sly ... and possibly the greatest thief in the world."
    } 
 */