JS: Number.isNaN

Number.isNaN ( number )

If number is NaN, return true, else false.

(NaN is a primitive value of number type that represents “not a number”.)

[see JS: NaN]

console.log ( Number.isNaN ( NaN ) ); // true

console.log ( Number.isNaN ( "NaN" ) ); // false
console.log ( Number.isNaN ( "3" ) ); // false
console.log ( Number.isNaN ( 3 ) ); // false
console.log ( Number.isNaN ( Infinity ) ); // false

Number.isNaN and the global isNaN are different.

isNaN converts argument to number first. Number.isNaN does not.

[see JS: isNaN]

Reference

ECMAScript® 2016 Language Specification#sec-number.isnan