Using jquery to hijack form values

I'm attempting to check my form values before submitting using jquery. When I attempt to check the values using alert() the values show as undefined.

 <form id="test" method ="get">           
 username<br>
 <br>
 <input type="text" name="firstfield">
 password 
 <input type="text" name="secondfield">
 <input type="submit" id="_click" value="click">
 </form>    
<script>
$(document).ready(function () {
$('#_click').click(function () {
var uname = $('#firstfield').val();
var pass = $('#secondfield').val();
alert(uname);
alert(pass);
});//click     
});//documentready
</script>