javascript - Switch 语句比较用户输入 Javascript

Question

我正在尝试这个简单的代码，似乎用户的输入没有经过所有比较并立即跳转到默认值。我猜 JS 正在将用户的输入作为字符串来代替。我确实尝试过 parseInt() 但没有成功。这是我的代码；

var number = prompt('What\'s your favority number?');

switch(number){
    case (number < 10):
        console.log('Your number is to small.');
        break;        
    case (number < 100):
        console.log('At least you\'re in the double digits.');
        break;
    case (number < 1000):
        console.log('Looks like you\'re in three digits.');
        break;
    default:
        console.log('Looks like you\'re in the fouth digits.');
}

Answer 1

使用true作为开关的表达式。

The switch statement evaluates an expression, matching the expression's value to a case clause, and executes statements associated with that case.[Ref]

switch 语句首先计算其表达式。然后它会查找第一个 case 子句，其表达式的计算结果与输入表达式的结果相同(使用严格比较，===)，并将控制权转移到该子句，执行关联的语句。 (如果多个案例与提供的值匹配，则选择第一个匹配的案例，即使这些案例彼此不相等。)。如果未找到匹配的 case 子句，程序将查找可选的 default 子句，如果找到，则将控制转移到该子句，执行相关语句。

var number = prompt('What\'s your favority number?');
number = Number(number); //Use `Number` to cast it as a number
switch (true) {
  //----^^^^
  case (number < 10):
    console.log('Your number is to small.');
    break;
  case (number < 100):
    console.log('At least you\'re in the double digits.');
    break;
  case (number < 1000):
    console.log('Looks like you\'re in three digits.');
    break;
  default:
    console.log('Looks like you\'re in the fouth digits.');
}

<script src="http://gh-canon.github.io/stack-snippet-console/console.min.js"></script>

编辑:根据 @bergi 的建议在评论中，if/else 级联是解决此问题的最佳方法。

var number = prompt('What\'s your favority number?');
number = Number(number); //Use `Number` to cast it as a number
if (number < 10)
  console.log('Your number is to small.');
else if (number < 100)
  console.log('At least you\'re in the double digits.');
else if (number < 1000)
  console.log('Looks like you\'re in three digits.');
else
  console.log('Looks like you\'re in the fouth digits.');