Javascript 函数在对象数组中调用？

Question

I googled a lot but no find a satisfying answer. Searching for a typing error in typescript faced the such code:

// @strict: false
let suits = ["hearts", "spades", "clubs", "diamonds"];

function pickCard(x: any): any {
  // Check to see if we're working with an object/array
  // if so, they gave us the deck and we'll pick the card
  if (typeof x == "object") {
    let pickedCard = Math.floor(Math.random() * x.length);
    return pickedCard;
  }
  // Otherwise just let them pick the card
  else if (typeof x == "number") {
    let pickedSuit = Math.floor(x / 13);
    return { suit: suits[pickedSuit], card: x % 13 };
  }
}

let myDeck = [
  { suit: "diamonds", card: 2 },
  { suit: "spades", card: 10 },
  { suit: "hearts", card: 4 },
];

let pickedCard1 = myDeck[pickCard(myDeck)];  //<--- HERE IS DOUBT
alert("card: " + pickedCard1.card + " of " + pickedCard1.suit);

let pickedCard2 = pickCard(15);
alert("card: " + pickedCard2.card + " of " + pickedCard2.suit);

I like to understand what such an expression is that? Am i calling a function inside an array of objects passing that array as a parameter? That's correct? And Why a cant call the function straight like this:

let pickedCard1 = pickCard(myDeck);

Always I do i got undefined as return. Sorry the jr question but i am trying to understand javascript better.Thanks guys

Answer 1

You're problem is that you've left something off of your object branch - you're returning number instead of a Card :

let pickedCard: number = Math.floor(Math.random() * x.length);
// This is really `pickedCardIndex`

Instead, check that the passed in value is an Array using Array.isArray and then index out of the array as your last step:

  if (Array.isArray(x)) {
    let pickedCardIndex = Math.floor(Math.random() * x.length);
    return x[pickedCardIndex];
  }