Check if a Number is NaN in Javascript

While working in javascript, we get a requirement to determine if a value is NaN in javascript. This article demonstrates easy ways to find out if a particular variable is NaN.
NaN in javascript is a global property with the value representing Not-a-Number.

1. Check if a Value is NaN using isNaN() method

The method isNaN(_value) is used to check if a value is a NaN or not. Here, _value is the value to test. This method will return true if a value is NaN. Else will return false.
The method Number.isNaN(_value) is used to check if a value is a NaN or not, and its type is Number. This method will return true if a value is NaN. Else will return false. Here, _value is the value to test.

Example:-

Check if the three values ‘Javascript123’, ‘1234’, 1234 are NaN or not.

Code:-

// create a new function checkIfNaN() 
function checkIfNaN(_variable)
{
    if(isNaN((_variable)))
    {
        console.log('Variable is NaN.');
    }
    else
    {
        console.log('Variable is NOT a NaN.');
    }
};
let dummyVariable1 = 'Javascript123';
let dummyVariable2 = '1234';
let dummyVariable3 = 1234;
//usage of function checkIfNaN() 
checkIfNaN(dummyVariable1);
checkIfNaN(dummyVariable2);
checkIfNaN(dummyVariable3);

Output:-

Variable is NaN.
Variable is NOT a NaN.
Variable is NOT a NaN.

Explanation:-

Within this method, the isNaN() method checks if a particular value is NaN or not if the value is NaN, “Variable is NaN.” is printed else “‘Variable is NOT a NaN.'” is printed on the console.

2. Check if a Value is NaN using value !== value

Example:-

Check if the three values ‘Javascript123’, ‘1234’, 1234 are NaN or not.

Code:-

// create a new function checkIfNaN() 
function checkIfNaN(_variable) 
{ 
    value = Number(_variable);
    return value !== value;
 };
let dummyVariable1 = 'Javascript123';
let dummyVariable2 = '1234';
let dummyVariable3 = 1234;
//usage of function checkIfNaN() 
checkIfNaN(dummyVariable1);
checkIfNaN(dummyVariable2);
checkIfNaN(dummyVariable3);

Output:-

true
false
false

Explanation:-

Here, in the above code, we are creating a function checkIfNaN() that will check if a value is NaN or not.
Within the method, we check if the value !== value, Only NaN will compare unequal to any other value including another NaN.

3. Check if a Value is NaN using toString()

Javascript’s Number.toString() method returns the string representation of the specified Number object.

Example:-

Check if the values ‘Javascript123’, ‘1234’ are NaN or not.

Code:-

// create a new function checkIfNaN() 
function checkIfNaN(_variable)
{
    return _variable.toString() === 'NaN' && 
    typeof _variable !== 'string' && 
    typeof _variable === 'number'
}

let dummyVariable1 = Number('Javascript123');
let dummyVariable2 = Number('1234');
//usage of function checkIfNaN() 
console.log(checkIfNaN(dummyVariable1))
console.log(checkIfNaN(dummyVariable2))

Output:-

true
false

Explanation:-

Here, in the above code, we are creating a function checkIfNaN() that will check if a value is NaN or not.
We check if the toString() on the Number value is ‘NaN’ and typeOf a variable is not a string but a number within the method. If all three conditions are fulfilled, true is returned, which means the value is NaN else false is returned.

4. Check if a Value is NaN using includes()

Javascript’s includes() method determines if a particular value is included in an array or not.

Example:-

Check if the three values ‘Javascript123’, ‘1234’ are NaN or not.

Code:-

// create a new function checkIfNaN() 
function checkIfNAN(_variable)
 {
    
    return [Number(_variable)].includes(NaN);  
  }

let dummyVariable1 = Number('Javascript123');
let dummyVariable2 = Number('1234');
//usage of function checkIfNaN() 
console.log(checkIfNaN(dummyVariable1))
console.log(checkIfNaN(dummyVariable2))

Output:-

true
false

Explanation:-

The above code shows another way to check if the value NaN is included in a number array. This array contains only one value: the variable passed as the argument into method checkIfNaN(). If the value is NaN true is returned else false is returned.

I hope this article helped you check if a value is NaN or not. Good Luck!!!