EJB 3.0 Database Persistence with Ajax in the UI - EJB 3.0 Database Persistence with Oracle Fusion Middleware 11g - page 288

As the callback event handler is processRequest , the processRequest()
function gets invoked when the value of the readyState property changes. In the
processRequest() function, the readyState property value is retrieved. If the
request has loaded completely, corresponding to readyState value 4 , and HTTP
status is "OK", we invoke a JavaScript function to process the response from
the server:
function processRequest(){
if(xmlHttpRequest.readyState==4){
if(xmlHttpRequest.status==200){
processResponse();
}
}
}
Processing the server response
In the processRequest() JavaScript function, if the HTTP request has loaded
completely, which corresponds to readyState property value 4 , and the
HTTP status is "OK", which corresponds to status property value 200 , the
processResponse() JavaScript function gets invoked. In the processResponse()
function, obtain the value of the responseXML property. This contains the XML
string that was set in the doGet() method of EJB3ClientServlet .
var xmlMessage=xmlHttpRequest.responseXML;
The responseXML property contains instructions in XML form about the validity of
the CatalogId value specified in the input form. Obtain the value of the <valid/>
element using the getElementsByTagName(string) method:
var valid=xmlMessage.getElementsByTagName("valid")[0].firstChild.
nodeValue;
If the <valid/> element is set to true , set the HTML validationMessage div to
"Catalog Id is Valid", and enable the Submit button in the input form, as shown below:
if(valid=="true"){
var validationMessage=document.getElementById("validationMessage");
validationMessage.innerHTML = "Catalog Id is Valid";
document.getElementById("submitForm").disabled = false;
}