JavaScript - Test for an integer

Question

I have a text field that allows a user to enter their age. I am trying to do some client-side validation on this field with JavaScript. I have server-side validation already

Answer 1

I did this to check for number and integer value

if(isNaN(field_value * 1) || (field_value % 1) != 0 ) not integer;
else integer;

Modular Divison

Example
1. 25.5 % 1 != 0 and ,
2. 25 % 1 == 0

And if(field_value * 1) NaN if string eg: 25,34 or abcd etc ... else integer or number