Prem Prem - 2 months ago 8
Javascript Question

how to check for datatype in node js- specifically for integer

I tried the following to check for the datatype (specifically for integer), but not working.

var i = "5";

if(Number(i) = 'NaN')
{
console.log('This is not number'));
}

Answer

I think of two ways to test for the type of a value:

Method 1:

You can use the isNaN javascript method, which determines if a value is NaN or not. But because in your case you are testing a numerical value converted to string, Javascript is trying to guess the type of the value and converts it to the number 5 which is not NaN. That's why if you console.log the result you will surprise that the code:

if (isNaN(i)) {
    console.log('This is not number');
}

would not return anything. That's why a better alternative would be the method 2.

Method 2:

You may use javascript typeof method to test the type of a variable or value

if (typeof i != "number") {
    console.log('This is not number');
}

Notice that i'm using double equal operator, because in this case the type of the value is a string but Javascript internally will convert to Number.

A more robust method to force the value to numerical type is to use Number.isNaN which is part of new Ecmascript 6 (Harmony) proposal, hence not widespread and fully supported by different vendors.