can't get javascript alert message to work when name entered can't be found

Hi
This is the xml file to go with html file
I just sent in a request for javascript in an html file. Can't get alert messages to work when name entered into input box not found.

<?xml version="1.0" encoding="utf-8"?>

<!DOCTYPE member SYSTEM "applydtd.dtd">

<?xml-stylesheet type="text/xsl" href="applyt.xsl" ?>



<customers>





   <person>

      <name>

        <first>John</first>

	    <last>Smith</last>

	  </name>

	  <address>

	     <street>123 Oak St</street>

	     <city>PERTH</city>

         <state>WA</state>

	     <postcode>4372</postcode>

	     <country>Australia</country>

		 <email>js@info.com.au</email>

      </address>

	  <phone>0754641323</phone>

   </person>

   <person>

	  <name>  

	    <first>Zack</first>

	    <last>Zwyker</last>

	  </name>

	  <address>

	    <street>368 Elm St</street>

	    <city>SYDNEY</city>

        <state>NSW</state>

	    <postcode>2000</postcode>

	    <country>Australia</country>

		<email>zz@info.com.au</email>

	  </address>

	  <phone>0478964234</phone>

	</person>

	<person>

	   <name> 	

		 <first>Albert</first>

	     <last>Aikens</last>

	   </name>	 

	   <address>

	   <street>368 Cedar St</street>

	     <city>BRISBANE</city>

         <state>QLD</state>

	     <postcode>7145</postcode>

	     <country>Australia</country>

		 <email>aa$info.com.au</email>

	    

	   </address>

	   <phone>0256897426></phone>

	</person>

	<person>

	<name>

		 <first>Michael</first> 

	     <last>Jones</last>

     </name>

	 <address>

	 <street>15 Cherry St</street>

	     <city>SYDNEY</city>

         <state>NSW</state>

	     <postcode>2000</postcode>

	     <country>Australia</country>

		 <email>jj@info.com.au</email>

	 </address>

   <phone>0297684321</phone>

   </person>

   </customers>