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

Question

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 1

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 out the result, you will be surprised that the code:

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

will not return anything. For this reason 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.

Answer 2

i have used it in this way and its working fine

quantity=prompt("Please enter the quantity","1"); quantity=parseInt(quantity); if (!isNaN( quantity )) {     totalAmount=itemPrice*quantity;  } return totalAmount;