我在JavaScript中遇到全局变量问题。我尝试做的是在函数外部声明变量,然后在函数内更改它,然后调用另一个函数。从我所读到的,这本应该有用,但它只是给我未定义。这是我正在制作的卡片绘制游戏的代码。
var randSuit;
function getRandCard() {
var randNum;
var randSuit;
var randVal;
randNum = Math.floor(Math.random()*13)+1;
if (randNum == 1) {
randVal = "2";
} else if (randNum == 2) {
randVal = "3";
} else if (randNum == 3) {
randVal = "4";
} else if (randNum == 4) {
randVal = "5";
} else if (randNum == 5) {
randVal = "6";
} else if (randNum == 6) {
randVal = "7";
} else if (randNum == 7) {
randVal = "8";
} else if (randNum == 8) {
randVal = "9";
} else if (randNum == 9) {
randVal = "10";
} else if (randNum == 10) {
randVal = "Jack";
} else if (randNum == 11) {
randVal = "Queen";
} else if (randNum == 12) {
randVal = "King";
} else if (randNum == 13) {
randVal = "Ace";
}
randNum = randNum = Math.floor(Math.random()*4)+1;
if (randNum == 1) {
randSuit = "Hearts";
} else if (randNum == 2) {
randSuit = "Clubs";
} else if (randNum == 3) {
randSuit = "Spades";
} else if (randNum == 4) {
randSuit = "Diamonds";
}
console.log(randSuit);
var randCard = (randVal + " of " + randSuit);
//Return the Value of the randomly chosen Card.
return (randCard);
}
//This function calls the random card from the function above, then applies logic to see if it's the same, then outputs the result.
$(function() {
$('#drawCard').click(function() {
var e = document.getElementById("faceValue");
var faceValue = e.options[e.selectedIndex].text;
var e = document.getElementById("suit");
var suit = e.options[e.selectedIndex].text;
$('#oneCardContainer').slideDown('slow');
var pickedCard = (faceValue + " of " + suit);
var randCard = getRandCard();
console.log (randSuit);
if (pickedCard == randCard) {
$("#oneCardResults").val("You Chose a " + pickedCard + " and got a " + randCard + ". \nYou Win!");
} else if (pickedCard != randCard) {
$("#oneCardResults").val("You Chose a " + pickedCard + " and got a " + randCard + ". \nYou Lose!");
}
});
});
这是我尝试的代码,我试图传递的变量是randSuit。我做错了什么?
答案 0 :(得分:3)
您正在定义一个名为randSuit
的全局变量,但也一个具有相同名称的局部变量。执行randSuit = randSuit;
时,实际上没有任何反应,因为左侧和右侧都引用了局部变量。你需要以不同的方式命名它们。
答案 1 :(得分:3)
JavaScript处理全局变量和局部变量的方式是,当解释器遇到标识符时,它会在当前作用域中搜索它(在您的情况下为getRandCard
),如果它找不到它 - 解释器上面有一个范围,如果在那里找不到它,那么上面有两个范围,依此类推。
randSuit = randSuit;
在这一行中,这些标识符都将引用相同的局部变量,因为解释器在本地范围内都找到它们,所以这条线路无效。
为了引用全局变量,您应该创建对其范围的引用:
var randSuit;
var that = this;
function getRandCard() {
...
}
然后,替换:
randSuit = randSuit;
使用:
that.randSuit = randSuit;
答案 2 :(得分:2)
您在函数内重新声明了randSuit
;该声明隐藏了全局randSuit
,因此您的函数正在修改自己的局部变量而不是全局变量。
答案 3 :(得分:1)
当您在函数内重新声明randsuit时,它会被私有化到该函数
var randSuit = 5; // not shared
function getRandCard() {
var randSuit = 3; // not shared
console.log(randSuit);
}
getRandCard();
console.log(randSuit);
如果您想共享randSuit
的输出,请不要重新声明变量
var randSuit = 5; // shared
function getRandCard() {
randSuit = 3; // shared
console.log(randSuit);
}
getRandCard();
console.log(randSuit);
更好的选择是模块化卡片变量和方法
var cardStack = (function () {
var randSuit; // protected from global
return {
getRandSuit: function () { return randSuit; }, // but still readable
getRandCard: function () { .... }
};
}());
var card = cardStack.getRandCard();
suit = cardStack.getRandSuit();
答案 4 :(得分:0)
试试这个,它是你的代码的缩短版本,应该可以工作:
var randSuit;
function getRandCard() {
var randNum, randVal;
var upperCards = ["Jack", "Queen", "King", "Ace"];
var suits = ["Hearts", "Clubs", "Spades", "Diamonds"];
randNum = Math.floor(Math.random()*13)+1;
(randNum < 10) ? randVal++ : randVal = upperCards[randNum-10];
randSuit = suits[Math.floor(Math.random()*4)];
// return the value of the randomly chosen card.
return (randVal + " of " + randSuit);
}
我使用了一些数组和一个三元运算符来大大缩短代码。我还删除了不受约束的本地randSuit
变量,该变量是作用域并覆盖了您的全局对象。
答案 5 :(得分:0)
如果要使用全局变量,则全局定义变量,不要在本地重新定义,只需在本地使用即可。当您在本地重新定义它时,您将创建一个具有相同名称的新局部变量,该变量取代该范围中的全局变量。
其余部分实际上是评论,但由于我无法在评论中有效地包含代码,因此我会将其作为答案的一部分发布。您真的需要在代码中应用DRY(不要重复自己)原则。这非常重复:
randNum = Math.floor(Math.random()*13)+1;
if (randNum == 1) {
randVal = "2";
} else if (randNum == 2) {
randVal = "3";
} else if (randNum == 3) {
randVal = "4";
} else if (randNum == 4) {
randVal = "5";
} else if (randNum == 5) {
randVal = "6";
} else if (randNum == 6) {
randVal = "7";
} else if (randNum == 7) {
randVal = "8";
} else if (randNum == 8) {
randVal = "9";
} else if (randNum == 9) {
randVal = "10";
} else if (randNum == 10) {
randVal = "Jack";
} else if (randNum == 11) {
randVal = "Queen";
} else if (randNum == 12) {
randVal = "King";
} else if (randNum == 13) {
randVal = "Ace";
}
randNum = randNum = Math.floor(Math.random()*4)+1;
if (randNum == 1) {
randSuit = "Hearts";
} else if (randNum == 2) {
randSuit = "Clubs";
} else if (randNum == 3) {
randSuit = "Spades";
} else if (randNum == 4) {
randSuit = "Diamonds";
}
可以用这个重复性较低的代码替换:
var cards = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "Jack", "Queen", "King", "Ace"];
randVal = cards[Math.floor(Math.random() * cards.length)];
var suits = ["Hearts", "Clubs", "Spades", "Diamonds"];
randSuit = suits[Math.floor(Math.random() * suits.length)];