JavaScript isNaN() Function

　JavaScript Global Properties/Function

GlobalisNaN()function that determines whether a value is an invalid number (non-numeric).

This function is different from the specificNumber.isNaN()Method.

The global isNaN() function converts the tested value to Number and then tests it.

Number.isNaN()It does not convert the value to Number and will not return true for any non-Number type.

Syntax:

isNaN(value)

isNaN(451);　　　//　false
isNaN(-3.13);　//　false
isNaN(3-1);　　　//　false
isNaN(0);　//　false
isNaN("451");　//　false
isNaN("Hello");　　　//　true
isNaN("20/12/2018");　　//　true
isNaN('');//　false
isNaN(true);　　//　false
isNaN(undefined);　//　true
isNaN('NaN');　//　true
isNaN(NaN);　　　//　true
isNaN(0　/　0);　//　true

Browser Compatibility

All browsers fully support the isNaN() function:

Parameter Value

Technical Details

More Examples

Check if the value is NaN using the isNaN() function:

var str = 'Hello world';
var ans = Number(str);　　　//Convert a string to a number
;if (isNaN(ans)) {
　　　;document.getElementById('result').innerHTML = ans;
}

　JavaScript Global Properties/Function