javascript - 开关盒中的 JS NaN 比较

Question

创建一个函数，无法理解我如何在 switch case 中进行比较，所以 NaN === case 为真并返回“输入数字是 Number.NaN”；

 function whatNumberIsIt(n){
      var str;
      switch (n) {
      case Number.MAX_VALUE : str = "Input number is Number.MAX_VALUE";
      break;
      case Number.MIN_VALUE : str = "Input number is Number.MIN_VALUE";
      break;
      case Number.NaN : str = "Input number is Number.NaN";
      break;
      case -Infinity : str = "Input number is Number.NEGATIVE_INFINITY";
      break;
      case Infinity : str = "Input number is Number.POSITIVE_INFINITY";
      break;
      default : str = "Input number is " + n;
      }
      return str;
    }
whatNumberIsIt(NaN)

Answer 1

比较switch语句中的isNaN，检查是否为false。这是代码:

  function whatNumberIsIt(n){
        var str;

        /**
         * The  !isNaN(n)  here is really the secret sauce.
         * This means the value has to be a real number before comparisons will 
         * even happen. That's why we're able to compare "false" in the switch... otherwise
         * this code wouldn't work.
         */
        switch (!isNaN(n) && n) {
            case Number.MAX_VALUE : 
                str = "Input number is Number.MAX_VALUE";
                break;

            case Number.MIN_VALUE : 
                str = "Input number is Number.MIN_VALUE";
                break;

            case false : 
                str = "Input number is Number.NaN";
                break;

            case -Infinity : 
                str = "Input number is Number.NEGATIVE_INFINITY";
                break;

            case Infinity : 
                str = "Input number is Number.POSITIVE_INFINITY";
                break;

            default : str = "Input number is " + n;
        }

        return str;
      }

  console.log( whatNumberIsIt("String") );
  console.log( whatNumberIsIt(NaN) );
  console.log( whatNumberIsIt(1) );
  console.log( whatNumberIsIt(Infinity) );
  console.log( whatNumberIsIt(-Infinity) );

fiddle :https://jsfiddle.net/87o83q2q/

这是您应该期望的输出:

Input number is Number.NaN
Input number is Number.NaN
Input number is 1
Input number is Number.POSITIVE_INFINITY
Input number is Number.NEGATIVE_INFINITY