What is Number.isNaN() in JavaScript?

Number.isNaN() is a Number method that checks if a value is NaN (Not A Number).

NaN in JavaScript is also a type of Number.

The Number.isNaN() method returns true if the value is of the type Number and is equal to NaN. Otherwise, the method returns false.

Number.isNaN() is different from the global isNaN() function. The global isNaN() function first converts the value to a Number, then tests it.

Number.isNaN() does not convert passed values to a Number and does not return true for any value that is not of the type Number.

Syntax

Number.isNaN(value);

Parameters

  • value: the value to be tested.

Return value

Number.isNaN() returns true if the passed value is NaN and is of the type Number. Otherwise, it returns false.

Code

In the example below, we pass some values to the Number.isNaN() function and log the results to the console.

console.log("Number.isNaN('NaN') ="+ Number.isNaN('NaN')) //false



console.log("Number.isNaN(NaN) ="+ Number.isNaN(NaN)) //true



console.log("Number.isNaN(0 / 0) ="+ Number.isNaN(0 / 0)) //true



console.log("Number.isNaN(222) ="+ Number.isNaN(222)) //false



console.log("Number.isNaN(-Math.pow(2, 4)) ="+ Number.isNaN(-Math.pow(2, 4))) //false



console.log("Number.isNaN(5-2) ="+ Number.isNaN(5-2)) //false



console.log("Number.isNaN(0) ="+ Number.isNaN(0)) //false



console.log("Number.isNaN('123') ="+ Number.isNaN('123')) //false



console.log("Number.isNaN('Hello') ="+ Number.isNaN('Hello')) //false



console.log("Number.isNaN('2005/12/12') ="+ Number.isNaN('2005/12/12')) //false



console.log("Number.isNaN('') ="+ Number.isNaN('')) //false



console.log("Number.isNaN(false) ="+ Number.isNaN(false)) //false



console.log("Number.isNaN(true) ="+ Number.isNaN(true)) //false



console.log("Number.isNaN(undefined) ="+ Number.isNaN(undefined)) //false



console.log("Number.isNaN({}) ="+ Number.isNaN({})) //false



console.log("Number.isNaN([]) ="+ Number.isNaN([])) //false



console.log("Number.isNaN(sqrt(-1)) ="+ Number.isNaN(Math.sqrt(-1))) // true

In the example above, the only cases that return true (other than the explicit NaN) are instances where we try to divide by zero or obtain the square root of a negative number. Both these instances return a Number of type NaN.

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