javascript window.event coming up null ?

Question

I am using a CustomValidator in ASP.NET as follows:

<asp:CustomValidator ID="cvComment" ControlToValidate="txtComment" Display="None"
        EnableClientScript="true" ClientValidationFunction="validateComment"
    runat="server" ></asp:CustomValidator>

And this is the function that gets called:

function validateComment(source, args) {
            var reComment = new RegExp("^[a-zA-Z0-9',!;?@#%*.\s]{1,1000}$");
            var validComment = reComment.test(window.event.srcElement.value);
            if (!validComment)
                alert("The comment has illegal characters");
            args.IsValid = validComment;
        }

Upon clicking the button that triggers the validator, the application breaks and I can see that the window.event property is null, so obviously there's a null reference trying to match the regEx. My question is why could the window.event be showing up as null? I could've sworn this was working before.

EDIT:

I have modified the function as such:

   var check = document.getElementById(source.id);
   var checky = check.attributes["controltovalidate"].value;
   var checkyo = document.getElementById(checky);
   var validHour = reOutHour.test(checkyo.value);
   if (!validHour)
        alert("The time is incorrectly formatted");
   args.IsValid = validHour;

Now this is working on Internet Explorer, but not on Firefox...

Answer 1

This is how I managed to solve my problem:

var check = document.getElementById(source.id);
   var checky = check.controltovalidate;
   var checkyo = document.getElementById(checky);
   var validHour = reOutHour.test(checkyo.value);
   if (!validHour)
        alert("The time is incorrectly formatted");
   args.IsValid = validHour;