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JavaScript Number NaN Property

  • Last Updated : 23 Jul, 2020

In JavaScript, NaN stands for Not a Number. It represents a value which is not a valid number. It can be used to check whether a number entered is a valid number or not a number. To assign a variable to NaN value, we can use one of the two following ways.

var a = NaN
var a = Number.NaN

Example: In this example, we will use JavaScript Number NaN Property.

var monthNumber = 14;
if (monthNumber < 1 || monthNumber > 12) {
    // Assigning monthNumber NaN as 
    // month number is not valid
    monthNumber = Number.NaN;
    console.log("Month number should be"
                + " between 1 and 12");
else {


We will see some examples of operations that return NaN.

Example 1: Whenever we try to parse a string or “undefined” to an int, it returns NaN.



Example 2: Whenever we try to find square root of a negative number using Math.sqrt function, it returns NaN.



Example 3: Whenever we try to make on operation on NaN, it returns NaN.

console.log(5 + NaN);


Example 4: Any indeterminate form also returns NaN.

console.log(0 * Infinity)


Example 5: Any operation other than addition on a string also results in NaN.



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