尝试洗牌时有 1 张牌未定义

Question

我正在尝试使用 html/css/javascript 制作二十一点游戏，但是当我触发我的 shuffleDeck function 时，我牌组中的 1 张牌变得未定义。

谁能解释一下这样做的原因？

 let cardValues = ["A", 1, 2, 3, 4, 5, 6, 7, 8, 9, "J", "Q", "K"]; let cardSuits = ["hearts", "spades", "clubs", "diamonds"]; let deck = new Array(); let players = new Array(); window.onload = function() { makeDeck(); shuffleDeck(deck); console.log(deck); } function makeDeck() { deck = new Array(); for (let i = 0; i < cardValues.length; i++) { for(let j = 0; j < cardSuits.length; j++) { let weight = parseInt(cardValues[i]);; if (cardValues[i] == "J" || cardValues[i] == "Q" || cardValues[i] == "K") { weight = 10; } else if (cardValues[i] == "A") { weight = 11; } let card = {cardValue: cardValues[i], cardSuit: cardSuits[j], cardWeight: weight} deck.push(card) } } } function shuffleDeck(deck) { for (let i = deck.length; i > 0; i--) { const j = Math.floor(Math.random() * (i + 1)); [deck[i], deck[j]] = [deck[j], deck[i]]; } }

Answer 1

问题在于你的洗牌循环：你let i = deck.length; 并使用i访问卡片组中的卡片 position。 但是当长度为52时，数组go的索引从0到51，所以你把undefined换成卡片。

这是一个非常常见的错误，因为数组索引从 0 而不是 1 开始。

因此，要更正此问题，只需将长度减一，或从 0 开始，而 i<length。

Answer 2

就像很多人已经提到的那样，您的洗牌循环需要从deck.length - 1开始：

function shuffleDeck(deck) {
  for (let i = deck.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [deck[i], deck[j]] = [deck[j], deck[i]];
  }
}

 let cardValues = ["A", 1, 2, 3, 4, 5, 6, 7, 8, 9, "J", "Q", "K"]; let cardSuits = ["hearts", "spades", "clubs", "diamonds"]; let deck = new Array(); let players = new Array(); window.onload = function() { makeDeck(); shuffleDeck(deck); console.log(deck); } function makeDeck() { deck = new Array(); for (let i = 0; i < cardValues.length; i++) { for(let j = 0; j < cardSuits.length; j++) { let weight = parseInt(cardValues[i]);; if (cardValues[i] == "J" || cardValues[i] == "Q" || cardValues[i] == "K") { weight = 10; } else if (cardValues[i] == "A") { weight = 11; } let card = {cardValue: cardValues[i], cardSuit: cardSuits[j], cardWeight: weight} deck.push(card) } } } function shuffleDeck(deck) { for (let i = deck.length - 1; i > 0; i--) { const j = Math.floor(Math.random() * (i + 1)); [deck[i], deck[j]] = [deck[j], deck[i]]; } }