JavaScript - Test for an integer

Question

Hello,

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 in place. However, I cannot seem to verify that the user enters an actual integer. I am currently trying the following code:

    function IsValidAge(value) {
        if (value.length == 0) {
            return false;
        }

        var intValue = parseInt(value);
        if (intValue == Number.NaN) {
            return false;
        }

        if (intValue <= 0)
        {
            return false;
        }
        return true;
    }

The odd thing is, I have entered individual characters into the textbox like "b" and this method returns true. How do I ensure that the user is only entering an integer?

Thank you

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.

Answer 2

use isNaN(n)

i.e.

if(isNaN(intValue))

in place of

if (intValue == Number.NaN)

Answer 3

For real int checking, use this:

function isInt(value) { 
    return !isNaN(parseInt(value)) && (parseFloat(value) == parseInt(value)); 
}

The problem with many int checks is that they return 'false' for 1.0, which is a valid integer. This method checks to make sure that the value of float and int parsing are equal, so for #.00 it will return true.