如何使用内部函数更改外部变量的值？

Question

在下面的代码中，当我使用函数 calcScore 时，外部变量 playerScore 和 computerScore 没有更新？如何使用函数更新它？据我了解，可以从内部范围更改外部变量的值，但为什么它在这里不起作用？    <script>        function playRound(playerSelection, computerSelection) {            playerSelection = playerSelection.toLowerCase();            computerSelection = computerSelection.toLowerCase();            if (playerSelection === computerSelection) {                return "draw";            }            else if (playerSelection === "rock"){                if (computerSelection === "scissors") return "win";                else if (computerSelection === "paper") return "lose";            }            else if (playerSelection === "paper"){                if (computerSelection === "scissors") return "lose";                else if (computerSelection === "rock") return "win";            }            else if (playerSelection === "scissors"){                if (computerSelection === "rock") return "lose";                else if (computerSelection === "paper") return "win";            }        }                function computerSelection() {            let selection = ["rock", "paper", "scissors"];            return selection[Math.floor(Math.random() * selection.length)];        }        function calcScore(result, playerScore, computerScore) {            if (result === "win") {                playerScore += 1;                console.log("win");            }            else if (result === "lose") {                computerScore += 1;                console.log("lose");            }            else if (result === "draw") {                playerScore += 1;                computerScore += 1;            }        }

Answer 1

Javascript 不会通过引用传递变量 - 因此您对函数所做的任何修改playerScore和computerScore内部修改calcScore()都只是该函数的局部修改。

您可以做的是制作playerScore全局computerScore变量。这样任何修改都将在全局范围内。或者，您可以calcScore()返回修改后的值。

使用全局方法：

    <script>

        let playerScore = 0;

        let computerScore = 0;

        function playRound(playerSelection, computerSelection) {

            playerSelection = playerSelection.toLowerCase();

            computerSelection = computerSelection.toLowerCase();

            if (playerSelection === computerSelection) {

                return "draw";

            }

            else if (playerSelection === "rock"){

                if (computerSelection === "scissors") return "win";

                else if (computerSelection === "paper") return "lose";

            }

            else if (playerSelection === "paper"){

                if (computerSelection === "scissors") return "lose";

                else if (computerSelection === "rock") return "win";

            }

            else if (playerSelection === "scissors"){

                if (computerSelection === "rock") return "lose";

                else if (computerSelection === "paper") return "win";

            }

        }

        

        function computerSelection() {

            let selection = ["rock", "paper", "scissors"];

            return selection[Math.floor(Math.random() * selection.length)];

        }

        function calcScore(result) {

            if (result === "win") {

                playerScore += 1;

                console.log("win");

            }

            else if (result === "lose") {

                computerScore += 1;

                console.log("lose");

            }

            else if (result === "draw") {

                playerScore += 1;

                computerScore += 1;

            }

        }

        function game() {

            for (let i = 1; i <= 5; i++) {

                let result = playRound(prompt("Select rock, paper, or scissors!"), computerSelection());

                calcScore(result);

                console.log(`You have ${playerScore} points! Computer has ${computerScore} points!`);

            }

            playerScore, computerScore = 0, 0;

        }

    </script>

替代方法：

    <script>

        function playRound(playerSelection, computerSelection) {

            playerSelection = playerSelection.toLowerCase();

            computerSelection = computerSelection.toLowerCase();

            if (playerSelection === computerSelection) {

                return "draw";

            }

            else if (playerSelection === "rock"){

                if (computerSelection === "scissors") return "win";

                else if (computerSelection === "paper") return "lose";

            }

            else if (playerSelection === "paper"){

                if (computerSelection === "scissors") return "lose";

                else if (computerSelection === "rock") return "win";

            }

            else if (playerSelection === "scissors"){

                if (computerSelection === "rock") return "lose";

                else if (computerSelection === "paper") return "win";

            }

        }

        

        function computerSelection() {

            let selection = ["rock", "paper", "scissors"];

            return selection[Math.floor(Math.random() * selection.length)];

        }

        function calcScore(result, playerScore, computerScore) {

            if (result === "win") {

                playerScore += 1;

                console.log("win");

            }

            else if (result === "lose") {

                computerScore += 1;

                console.log("lose");

            }

            else if (result === "draw") {

                playerScore += 1;

                computerScore += 1;

            }

            return [playerScore, computerScore];

        }

        function game() {

            let playerScore = 0;

            let computerScore = 0;

            for (let i = 1; i <= 5; i++) {

                let result = playRound(prompt("Select rock, paper, or scissors!"), computerSelection());

                let scores = calcScore(result, playerScore, computerScore);

                playerScore += scores[0];

                computerScore += scores[1]; 

                console.log(`You have ${playerScore} points! Computer has ${computerScore} points!`);

            }

            playerScore, computerScore = 0, 0;

        }

    </script>

Answer 2

你两次定义了这两个变量，所以现在我很困惑。您是否希望能够在游戏函数中重用这些变量而无需重新定义它们？因为如果是这样的话，那么它们应该是全局变量而不是函数参数（您将无法在该函数之外使用函数参数中定义的变量）。