// XmlHttp constructor can receive request settings:
// url - the server url
// contentType - request content type
// type - request type (default is GET)
// data - optional request parameters
// async - whether the request is asynchronous (default is true)
// showErrors - display errors
// complete - the callback function to call when the request
// completes
function XmlHttp(settings)
{
// store the settings object in a class property
this.settings = settings;
// override default settings with those received as parameter
// the default url points to the current page
var url = location.href;
if (settings.url)
url = settings.url;
// the default content type is the content type for forms
var contentType = "application/x-www-form-urlencoded";
if (settings.contentType)
contentType = settings.contentType;
// by default the request is done through GET
var type = "GET";
if(settings.type)
type = settings.type;
// by default there are no parameters sent
var data = null;
if(settings.data)
{
data = settings.data;
// if we go through GET we properly adjust the URL
if(type == "GET")
url = url + "?" + data;
}
// by default the postback is asynchronous
var async = true;
if(settings.async)
async = settings.async;
// by default we show all the infrastructure errors
var showErrors = true;
if(settings.showErrors)
showErrors = settings.showErrors;
// create the XmlHttpRequest object
var xhr = XmlHttp.create();
// set the postback properties
xhr.open(type, url, async);
xhr.onreadystatechange = onreadystatechange;
xhr.setRequestHeader("Content-Type", contentType);
xhr.send(data);
// the function that displays errors
function displayError(message)
{
// ignore errors if showErrors is false
if (showErrors)
{
// display error message
alert("Error encountered: n" + message);
}
}
// the function that reads the server response
function readResponse()
{
try
{
// retrieve the response content type
var contentType = xhr.getResponseHeader("Content-Type");
// build the json object if the response has one
if (contentType == "application/json")
{
response = JSON.parse(xhr.responseText);
}
// get the DOM element if the response is XML
else if (contentType == "text/xml")
{
response = xhr.responseXml;
}
// by default get the response as text
else
{
response = xhr.responseText;
}
// call the callback function if any
if (settings.complete)
settings.complete (xhr, response, xhr.status);
}
catch (e)
{
displayError(e.toString());
}
}
// called when the request state changes
function onreadystatechange()
{
// when readyState is 4, we read the server response
if (xhr.readyState == 4)
{
// continue only if HTTP status is "OK"
if (xhr.status == 200)
{
try
{
// read the response from the server
readResponse();
}
catch(e)
{
// display error message
displayError(e.toString());
}
}
else
{
// display error message
displayError(xhr.statusText);
}
}
}
}
// static method that returns a new XMLHttpRequest object
XmlHttp.create = function()
{
// will store the reference to the XMLHttpRequest object
var xmlHttp;
// create the XMLHttpRequest object
try
{
// assume IE7 or newer or other modern browsers
xmlHttp = new XMLHttpRequest();
}
catch(e)
{
// assume IE6 or older
try
{
xmlHttp = new ActiveXObject("Microsoft.XMLHttp");
}
catch(e) { }
}
// return the created object or display an error message
if (!xmlHttp)
alert("Error creating the XMLHttpRequest object.");
else
return xmlHttp;
}