javascript - 加等于运算符(operator)错误

Question

您好，我正在尝试使用 += 来增加余额值。我现在明白在java脚本中使用+=是按引用传递，但是我如何使用它按值传递。

alert("Welcome to the Online Bank Teller");

        var balance = 100.00;
        var amount;
        var run = true;

        do{

            var pick = prompt("Make a selection...\n1-Check Balance, 2-Deposit, 3-Withdraw, 4-Quit");

            if(pick == 1){alert("Your balance is: $" + balance.toFixed(2));}
            else if(pick == 2){ 
                    amount = prompt("Enter the amount you want to deposit: $");

                    if(amount > 1000){alert("You can only enter up to $1000 per deposit!");}
      Right here--->balance += amount;
                    alert("Your new balance: $" + balance.toFixed(2));
            }
            else if(pick == 3){ 
                    amount = prompt("Enter the amount you want to withdraw: $");

                    if(amount > balance){alert("Amount exceeded account balance!");}
                    else if(amount > 500){alert("The max you can take out is up to $500 per withdraw!");}
                    else if (amount <= balance){
                            balance -= amount;
                            alert("Your new balance: $" + balance.toFixed(2));
                    }                               
            } 
            else if(pick == 4){run = false;}
            else{alert("Not a valid choice!");}

        }while(run)

当用户输入新的存款时，如何让它改变变量内部的值。

我明白了

Your balance is: $10022

而不是

Your balance is: $122

提前致谢...

Answer 1

对从提示中获取的每个金额使用parseInt()函数

amount = parseInt(prompt("Enter the amount you want to deposit: $"), 10);

DEMO