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

var intRegex = /^\d+$/;
if(intRegex.test(someNumber)) {
   alert('I am an int');
   ...
}

That will absolutely, positively fail if the user enters anything other than an nonnegative integer.