Oleksandr Buchek - 1 year ago 83
Javascript Question

# JS NaN comparison in switch cases

Making a function and can`t understand how would I make a comparison in switch case, so NaN === case goes true and return "Input number is 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)
``````

Compare `isNaN` in the switch statement, check for false. Here's the code:

``````  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) );
``````

Here's the output you should expect:

``````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
``````