interface Card {

  suit: string;

  card: number;

}

interface Deck {

  suits: string[];

  cards: number[];

  createCardPicker(this: Deck): () => Card;

}

let deck: Deck = {

  suits: ["hearts", "spades", "clubs", "diamonds"],

  cards: Array(52),

  // NOTE: The function now explicitly specifies that its callee must be of type Deck

  createCardPicker: function (this: Deck) {

    return () => {

      let pickedCard = Math.floor(Math.random() * 52);

      let pickedSuit = Math.floor(pickedCard / 13);

      return { suit: this.suits[pickedSuit], card: pickedCard % 13 };

    };

  },

};

let cardPicker = deck.createCardPicker();

let pickedCard = cardPicker();

alert("card: " + pickedCard.card + " of " + pickedCard.suit);

Try