Urgent about javascript ,Thanks

Hi,
If there's a webpage have 1)a Textbox 2)A form button
If I want : if the textbox havent inputted anything, the form button is disable, how can I do this? Thanks.

Also, it must work in Netscape, I know a method to work in IE but not in Netscape, as follows:
<script language="javascript">
function test() {
if (document.form1.textbox.value!="")
document.form1.button.disabled = false;
else
document.form1.button.disabled = true;
}
</script>
<form name="form1">
<input type="text" value="" name="textbox" onKeyup="test()">
<input type="button" name="button" value="Button" disabled>
</form>

Do you want 'disabled' or 'doesn't work'?
'Disabled' I'm not so sure on, I'll have a look for the compatibility (it might not be supported in NS...
'Doesn't work' you can always achieve with client side validation.
Dave

http://www.faqts.com/knowledge_base/view.phtml/aid/1747/fid/309
Hope this will help