JavaScript - Text Box Value = Script

var xmlHttp;

function ajax_compatible() 
{
   // Post: Returns an object if browser is AJAX compatible else false.
   
   if (window.XMLHttpRequest)
   {
      // users web browser can support AJAX
      return ( new XMLHttpRequest() );
   }
   else if (window.ActiveXObject)
   {
      // users web browser is IE6 and IE5
      return ( new ActiveXObject("Microsoft.XMLHTTP") );
   }
   else {
       alert("Unfortunately your browser does not support AJAX.");
      return null;
   }
}


function get_cookie(cookie_name) 
{ 
	if (document.cookie.length > 0) 
	{ 
	  c_start = document.cookie.indexOf(cookie_name + "="); 
	  
	  if (c_start != -1) 
	  {  
		c_start = c_start + cookie_name.length+1; 
		c_end   = document.cookie.indexOf(";",c_start) 
		
		if (c_end == -1) 
		{
		   c_end = document.cookie.length;
		}
		
		return unescape(document.cookie.substring(c_start,c_end)) 
	  }  
	} 
	return "" 
} 


function add_comment()
{
   // Post: Add user comment & rating to database and update new table row.
   // DO WE NEED TO SEND COOKIE ASWELL OR IS IT ALREADY DONE???
   
   xmlHttp = ajax_compatible();
   
   if (xmlHttp == null) {
       return;
   }
   
   var url = 'http://localhost:8000/cgi-bin/main.py';
   
   alert("add_comment() running");
   
   // Extract CGI variables to pass onto python script
   var id = document.getElementById('videoID').value;
   var video_id = 'videoID=' + id;
   var rating   = 'rating=' + document.getElementsByName('rating').value;
   var comment  = 'comment=' + document.getElementById('comment').value;
   var add_rating = 'addRating=' + document.getElementById('addRating').value;
   //var cookie = document.cookie;
   
   cgi_var = video_id + '&' + rating + '&' + comment + '&' + add_rating; // + '&' + cookie;
   
   // open python script 
   xmlHttp.open('POST',url,true);
   xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded'); 
	   
   // Error is in below line
   xmlHttp.onreadystatechange = state_changed(id); 
   // if I use the following line then it works
   // xmlHttp.onreadystatechange = test; 
   xmlHttp.send(cgi_var);
}


function state_changed(element_id)
{
   // Post: Use one function that will be used for each page update.
   //       This function sends the text returned by the python server script
   //       onto the browser(HTML element with the id 'element_id') to be displayed.
   
   if (xmlHttp.readyState == 4) 
	{
	   document.getElementById(element_id).innerHTML = xmlHttp.responseText;
	}

}

function test()
{
   // Post: used to test where the problem occurs
   // This function works
   
   if (xmlHttp.readyState == 4) 
	{
	   document.getElementById('result').innerHTML = xmlHttp.responseText;
	}

}

<script language="javascript">

fields = 1;

function addMore() {

if (fields = 1) {

document.getElementById('addedMore').innerHTML = "<input type='text' name='field2' size='25' /> <span>Field 2.</span>";

fields = 2;

} else if (fields = 2) {

document.getElementById('addedMore').innerHTML = "<input type='text' name='field3' size='25' /> <span>Field 3.</span>";
fields = 3;

} else {

document.getElementById('addedMore').innerHTML = "Only 3 fields are allowed.";
document.form.add.disabled=true;

}

}

</script>

<input type="text" name="field1" size="25" /> <span>Field 1.</span>
<div id="addedMore"></div>
<p class="addMore"><form name="add"><a onclick="addMore()">Add another field.</a></form></p>

<script type="text/javascript">
function enlarge(imageNum)
{
var numToString = "";
if(parseInt(imageNum) < 10){
numToString = "0" + imageNum;
}
else
{
numToString = imageNum + "";
}
window.open("images/LgScreenshot"+numToString+".jpg","Screenshot "+imageNum,"status=0,height=675,width=900,resizable=0");
}
</script>

<script type="text/javascript" src="script.js ?param1=val1&param2=val2&etc ">