Question

我正在通过一个快速的二十一点游戏来学习javascript的一些基础知识，但我不明白为什么我的代码无法正常工作。显然我不了解JavaScript的基本原理

const types = [
  "1",
  "2",
  "3",
  "4",
  "5",
  "6",
  "7",
  "8",
  "9",
  "10",
  "J",
  "Q",
  "K",
  "A"
];
const suite = ["Hearts", "Spades", "Clubs", "Diamonds"];
const draw = () => Math.floor(Math.random() * 52);
let cards = makeDeck(suite, types);
let score = 0;

//creates the card object
function Card(type, rank) {
  this.type = type;
  this.rank = rank;
}

//creates an array with every card
function makeDeck(suite, types) {
  let cards = [];
  let value = 0;
  for (let i = 0; i < suite.length; i++) {
    for (let j = 0; j < types.length; j++) {
      cards.push(new Card(types[j], suite[i]));
    }
  }

  return cards;
}


function determine(Card, score) {
  let test = 11;
  if (/^\d+$/.test(Card.type)) {
    test = parseInt(Card.type);
    console.log(test);
    return test;
  } else {
    if (Card.type === "J" || "Q" || "K") {
      test = 10;
      return test;
    } else {
      if (score > 11) {
        test = 2;
        return test;
      }
    }

    return test;
  }
}

function game() {
  let gameDeck = cards;
  let card1 = gameDeck[draw()];
  let card2 = gameDeck[draw()];
  let card3 = gameDeck[draw()];
  let card4 = gameDeck[draw()];
  let scorePlayer = determine(card1, score) + determine(card2, score);
  let scoreDealer = determine(card3, score) + determine(card4, score);

  console.log(scoreDealer);
  console.log(scorePlayer);
  console.log(card1, card2, card3, card4);
}


game();

因此，我关心的是确定功能，该功能似乎无法按我预期的方式工作。我还没有实现真正的评分功能，但目前还不应该有太大的不同。我对let和const的使用是否有误？

Answer 1

if (Card.type === "J" || "Q" || "K") {
      test = 10;
      return test;
    }

无论“ Card.type”的值如何，该块始终为true。因为当Card.type不等于“ J”时，javascript会检查if("Q")始终为true。同样，if("K")也是如此。所有这些都是Javascript中的真实值。 Javascript有7个虚假条件，但所有其他条件均成立。在浏览器控制台中尝试使用此代码段。

    if("Q") {
        console.log("This statement is true always")
    }

请参考这两个链接以更好地理解All falsey values in JavaScript 和https://developer.mozilla.org/en-US/docs/Glossary/Falsy

了解JS编译问题

1 个答案: