Which is more suitable to use, isNaN or Number.isNaN() in JavaScript

In JavaScript, NaN is a valid value of the number type.

console.log(typeof NaN); // number 

When prompted to verify if a value matches NaN or not, you’ll encounter an irony: NaN doesn’t equate to itself. Therefore, standard equality comparisons are ineffective for checking NaN values.

if(NaN === NaN){
    console.log("NaN is equal to NaN");

}
else {
    console.log("NaN is not equal to NaN");

}

Besides, NaN is neither greater nor smaller than any other numeric value.

if(NaN === NaN){
    console.log("NaN is equal to NaN");

}
else {
    console.log("NaN is not equal to NaN");

}
if(NaN > NaN){
    console.log("NaN is Greater to NaN");

}
else {
    console.log("NaN is not Greater to NaN");

}

if(NaN < NaN){
    console.log("NaN is Smaller to NaN");

}
else {
    console.log("NaN is not Samller to NaN");

}

You get below output,

So, how do you check for the value of NaN? There are two ways to check for the value of NaN.

• isNaN()
• Number.isNaN()

Let us first learn about isNaN().  This function checks for the NaN in these two steps,

• Converts the given value to a number
• Check whether the converted value is NaN or not.

So, if you check on the following

console.log(isNaN(undefined));  // true 
console.log(isNaN(null)); // false
console.log(isNaN(true)); // false 
console.log(isNaN("100")); // false 

Surprisingly, it returns false for null, true, and “100” because it can convert them to a number.

The other approach is using the Number.isNaN().  

1. It does not convert the given value to a number
2. It directly checks whether the given value is NaN or not

So, if you check the following,

console.log(Number.isNaN(undefined)); // false
console.log(Number.isNaN(null)); // false
console.log(Number.isNaN(true)); // false
console.log(Number.isNaN("100")); // false

You will get the expected result.  My suggestion is to use Number.isNaN() to check for the value of NaN.