select options manuplation of javascript

<form action="" method="get" accept-charset="utf-8">
<strong>Single Robot Choice:</strong>  
<select name="robot" id="robot"> 
      <option value="1">Security</option> 
      <option value="2">Trainer</option> 
      <option value="3">Friend</option> 
      <option value="4">Cook</option> 
</select> 
<br /><br /> 
<strong>Multiple Robot Choice:</strong>  
<select name="robotMulti" id="robotMulti" size="4" multiple="multiple"> 
      <option value="a">Security</option> 
      <option value="g">Trainer</option> 
      <option value="s">Friend</option> 
      <option value="d">Cook</option> 
</select>

<input type='button' value='-' name='button1'>
</form>

<script type="text/javascript" charset="utf-8">
 function doc (argument) {
  document.write(argument);
  document.write("<br />\n");
 }
 
 function selectedItems (obj) {
  var o = obj.options;
  var s = '';
  for(var i in o) {
   if(o[i].selected){
    s += 'index="' + i + '": selected options text="' + o[i].text + '", selected options value="' + o[i].value + '"; ';
   }
  }
  alert(s);
 }
 
 var select1 = document.forms[0].robot
 var select2 = document.forms[0].robotMulti
 
 // doc(select1);
 // alert(select2.multiple);
 
 select1.onchange = function () {
  alert('selected text = "' + select1.options[select1.selectedIndex].text + '"; selected index="' + select1.selectedIndex + '"; option index ="' + select1.options[select1.selectedIndex].index + '" ');
 }
 
 document.forms[0].button1.onclick = function() {
  selectedItems(select2);
 }

</script>