在大学里用JavaScript做第一门课程。必须改变扑克游戏以增加跑步总数。最后添加了功能updatetotalWinnings，但无法正常工作。多年来一直在尝试不同的东西！ html标头中调用的Javascript文件。开始时将totalWinnings设置为100。 html“总计”行中的输出未定义。 'coin'和'winnings'html行给出正确的输出。请帮忙！
function determineWinnings() {
var moneyStr;
var winnings;
var money = [0, 10, 20, 30, 60, 40, 70, 50, 80, 90];
moneyStr += "<BR>" + "Winnings for this hand are: " + money[winType] + " cents";
winnings = money[winType];
document.getElementById("money").innerHTML = "<p> " + moneyStr + "</p>"; // This prints "Winnings for this hand are: money[winType] "
document.getElementById("coin").innerHTML = "<p> " + winnings + "</p>";
document.getElementById("winnings").src = "coins/" + money[winType] + ".png";
}
function updatetotalWinnings(winnings, totalWinnings) {
if (winnings > 0) {
totalWinnings += winnings;
}
document.getElementById("total").innerHTML = "<p> " + totalWinnings + "</p>";
}
非常感谢Mike的明确解释，也感谢Caleb，Mottie和mhodges的回应。我已经按照Mike和Caleb的建议做了，并宣布totalWinnings = 100;功能上方（请参阅下文）。我还尝试过将这行代码放在定义了函数poker（）的javascript程序的开头（请参见下文），两者均无效。我还根据Mottie的要求包含了html。
var handSize, suits, values, cards, result, winType; // Defines global variables handsize, suits, values, cards, result, wintype.
var moneyStr, money, winnings;
var totalWinnings = 100;
function poker()
{
handSize = 5;
suits = new Array(handSize);
values = new Array(handSize);
cards = new Array(handSize);
result = "";
generateUniqueHandOfCards();
determineSuitsAndValues();
orderValuesInDescendingSequence();
determineCardDescriptions();
evaluateHandOfCards();
determineWinType();
determineWinnings();
updatetotalWinnings();
//document.write(result);
document.getElementById("cardPara").innerHTML = result;
document.getElementById("total").innerHTML = "<p>" + totalWinnings + "</p>";
document.getElementById("total2").innerHTML = updatetotalWinnings();
}
function determineWinnings()
{
var moneyStr;
var money = [0, 10, 20, 30, 60, 40, 70, 50, 80, 90];
moneyStr += "<BR>" + "Winnings for this hand are: " + money[winType] + " cents"; // Note money[winType] is a number giving the cents won.
winnings = money[winType];
// document.getElementById("money").innerHTML = "<p> " + moneyStr + "</p>"; // This prints "Winnings for this hand are: money[winType] "
document.getElementById("coin").innerHTML = "<p> " + winnings + "</p>"; // Prints winnings without accompanying text.
document.getElementById("winning").src = "coins/" + money[winType] + ".png"; // Note since money[winType] is not a string it is not in quotes.
}
var totalWinnings = 100;
function updatetotalWinnings(winnings)
{
if (winnings > 0){
totalWinnings += winnings;
}
}
<!DOCTYPE html>
<html>
<head><title>Assignment 2 Poker Game</title>
<script src= "PokerAssignment10.js">
</script>
</head>
<body>
<button id="button1" onclick="poker()"> Run Poker Game! </button>
<p> </p> <!-- Inserts a blank paragraph after the Run Poker Game! button -->
<!-- Lines 21-25 initially put five card_back images side by side.
Once the function poker has run by clicking on "Run Poker Game" button,
the id="card"+i flag is used to put the image for each card dealt side-by-side.
-->
<img id="card0" src="card_back.png" alt="card_back" width="100" height="145">
<img id="card1" src="card_back.png" alt="card_back" width="100" height="145">
<img id="card2" src="card_back.png" alt="card_back" width="100" height="145">
<img id="card3" src="card_back.png" alt="card_back" width="100" height="145">
<img id="card4" src="card_back.png" alt="card_back" width="100" height="145">
<p> </p>
<p> </p>
<p id="cardPara"> Hand type dealt will appear here </p>
<p id="money"> </p>
<p id="coin"> </p>
<p>
<img id="winning" alt="Winnings will appear here" height="60" >
<!-- Note leaving out the img src= attribute, html lists the alt= text string "Winnings will appear here" instead -->
<!-- Using document.getElementById("winning").src = source location in javascript then replaces text string with image -->
</p>
<p id="total"> </p>
<p id="total2"> </p>
</body>
</html>
我仍然在HTML页面的id =“ total”中的totalWinnings中显示100，而在HTML页面的id =“ total2”中的updatetotalWinnings中未显示。
最佳答案
这样的情况向您展示了不同范围的有用性。考虑以下示例：
function add2() {
var total = 0;
total += 2;
console.log(total);
}
在这种情况下，它将始终打印
2，因为total是在函数内部声明的。如果我们将变量传递给函数，也会发生同样的问题。function add2(total) {
total += 2;
console.log(total);
}
var total = 0;
add2(total); // 2
add2(total); // 2
console.log(total); // 0
在这种情况下，您传入了一个外部变量，但未更新。那是怎么回事？在Javascript中，数字以“按值”形式传递。这意味着将变量值的副本传递到函数中。由于是副本，因此不会更新原始变量。对象/数组“通过引用”传递。它与“按价值”的区别不在此答案的范围之内，但将来有必要知道。
那么我们如何获得持久的价值呢？一种方法是在函数外部声明变量，然后在函数内部引用它。
var total = 0;
function add2() {
total += 2;
console.log(total);
}
add2(); // 2
add2(); // 4
add2(); // 6
之所以可行，是因为我们每次调用函数时都引用实际的原始变量，而不是创建副本或创建新变量。
因此，解决问题的最简单方法是在函数外部声明
totalWinnings，然后在其他函数内部引用它。