使用 Switch 语句的 JavaScript - 未获得预期输出

Question

我对此很陌生，还有很多东西要学习。我在这段 JavaScript 中使用了 Switch 语句，但没有得到 document.write 行的预期输出。如有任何帮助、意见和建议，我们将不胜感激。 - 谢谢!

            <script type="text/javascript">

            var myAge = Number(prompt("Enter your age", 30));
            myAge = parseInt(myAge);

            switch (myAge)
            {
                case (myAge  >= 0 && myAge <= 10):
                    document.write("myAge is between 0 and 10");
                    break;

                case (!(myAge >= 0 && myAge <=10)):
                    document.write ("myAge is NOT between 0 and 10 <br />");
                    break;

                case (myAge >= 80 || myAge <= 10):
                    document.write ("myAge is 80 or above OR 10 or below <br />");
                    break;

                case (myAge >= 30 && myAge <=39 || (myAge >= 80 && myAge <= 89)):
                    document.write("myAge is between 30 and 39 or myAge is between 80 and 89");
                    break;

                default:
                    document.write("You did not enter a number.  Please enter a number.");
                    break;
            }       

            document.write("<BR>Execution continues here");


        </script>

这是我仅使用“if”编写的内容。

        <script type="text/javascript">

        var myAge = Number(prompt("Enter your age", 30));

        if (myAge  >= 0 && myAge <= 10)
        {
            document.write ("myAge is between 0 and 10 <br />");
        }

        if (!(myAge >= 0 && myAge <=10))
        {
            document.write ("myAge is NOT between 0 and 10 <br />");
        }

        if (myAge >= 80 || myAge <= 10)
        {
            document.write ("myAge is 80 or above OR 10 or below <br />");
        }

        if (myAge >= 30 && myAge <=39 || (myAge >= 80 && myAge <= 89))
        {
            document.write("myAge is between 30 and 39 or myAge is between 80 and 89");
        }   


    </script>

这是我必须引用的使用“switch”的示例代码。

<script type="text/javascript">

var secretNumber = prompt("Pick a number between 1 and 5:", "");
secretNumber = parseInt(secretNumber);

switch (secretNumber)
{
case 1:
   document.write("Too low!");
   break;

case 2:
   document.write("Too low!");
   break;

case 3:
   document.write("You guessed the secret number!");
   break;

case 4:
   document.write("Too high!");
   break;

case 5:
   document.write("Too high!");
   break;

default:
   document.write("You did not enter a number between 1 and 5.");
   break;
}
document.write("<BR>Execution continues here");

</script>

Answer 1

您需要重新考虑 case 表达式中的逻辑。

让我在您的代码中进行替换，以说明错误

var test = myAge >= 0 && myAge <= 10;
if (test) {
   ...
} else if (!test) {
   ...
} else {
   // WILL NEVER BE RUN
}

如果您想使用 switch 语句，您必须了解您正在使用的数据背后的类型。

true : Boolean
false : Boolean
9 : Number
1.0 : Number

在下面的示例中，v 必须与 value1 和 value2 具有相同的类型。

switch(v)
{
   case (value1):
   ...       
   case (value2):
   ...
}

问题是以下类型与您的示例不匹配。

v = Number
value1 = Boolean
value2 = Boolean