开关案例中的if / else语句

Question

我是js /编程新手，只是使用提示制作一个简单的计算器。 我试图验证输入的是数字而不是字符串。 我试过了

var operatorType = prompt("Do you want to add, subtract, multiply or divide?").toLowerCase();

switch (operatorType) {
    case 'add':
        var i = prompt("Enter your first number");
        var j = prompt("Enter your second number");
        if (isNaN(i) === false) && (isNaN(j) === false) {
            document.write(i+" plus "+j+" equals "+(i+j));
        } else {
            document.write("You didn't enter two numbers.");
        }
    break;

和if (i != 'string') && (j != 'string')但我不断收到“意外令牌&&”。 我查了一下，在一个案例中是否有效，所以我不确定自己在做什么错。

完整的代码（如果有帮助）

var operatorType = prompt("Do you want to add, subtract, multiply or divide?").toLowerCase();

switch (operatorType) {
    case 'add':
        var i = prompt("Enter your first number");
        var j = prompt("Enter your second number");
        if (isNaN(i) === false) && (isNaN(j) === false) {
            document.write(i+" plus "+j+" equals "+(i+j));
        } else {
            document.write("You didn't enter two numbers.");
        }
    break;

    case 'subtract':
        var i = prompt("Enter your first number");
        var j = prompt("Enter your second number");
        document.write(i+" minus "+j+" equals "+(i-j));
    break;

    case 'multiply':
        var i = prompt("Enter your first number");
        var j = prompt("Enter your second number");
        document.write(i+" multiplied by "+j+" equals "+(i*j));
    break;

    case 'divide':
        var i = prompt("Enter your first number");
        var j = prompt("Enter your second number");
        document.write(i+" divided by "+j+" equals "+(i/j));
    break;

    default:
        document.write("Please enter whether you want to add, subtract, multiply or divide.");
    break;
}

Answer 1

您的括号位置错误，导致语法错误。 您需要在此行中移动括号才能更改为：

if (isNaN(i) === false) && (isNaN(j) === false) {

这样就变成：

if (isNaN(i) === false && (isNaN(j) === false)) {

您还需要将字符串转换为数字，以便您的代码真正添加/等，而不是串联文本。