Validate function in java script and upload box

I have a telerik rad uploader and a button to upload the file. I want to validate with some client side validation on the OnClientClick. Appears that when the page loads I suppose it's hitting my validate function and not making the uploader control. What could be the issue. Below is how I'm trying to obtain the data in the uploader:
var myfile = document.getElementById('<%=fileuploader.ClientID%').value;
...