// stores the reference to the XMLHttpRequest object
var xmlHttp = createXmlHttpRequestObject();
// retrieves the XMLHttpRequest object
function createXmlHttpRequestObject()
{
	// will store the reference to the XMLHttpRequest object
	var xmlHttp;
	// if running Internet Explorer
	if(window.ActiveXObject)
	{
		try
		{
			xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
		}
		catch (e)
		{
			xmlHttp = false;
		}
	}
	// if running Mozilla or other browsers
	else
	{
		try
		{
			xmlHttp = new XMLHttpRequest();
		}
		catch (e)
		{
			xmlHttp = false;
		}
	}
	// return the created object or display an error message
	if (!xmlHttp)
		alert("Error creating the XMLHttpRequest object.");
	else
		return xmlHttp;
}

// make asynchronous HTTP request using the XMLHttpRequest object
function subscriber()
{
	document.getElementById("errorMsg").innerHTML = 'wait...';
	if(isNull(document.frmSubscriber.name.value))
	{
		document.getElementById("errorMsg").innerHTML = 'Please enter your name';
		document.frmSubscriber.name.focus();
		return;
	}
	if(!isEmail(document.frmSubscriber.email.value))
	{
		document.getElementById("errorMsg").innerHTML = 'Please enter your valid email id.';
		document.frmSubscriber.email.focus();
		return;
	}
	// proceed only if the xmlHttp object isn't busy
	if (xmlHttp.readyState == 4 || xmlHttp.readyState == 0)
	{
		// execute the quickstart.php page from the server
		xmlHttp.open("GET", "subscriber_by_ajax.php?email=" + document.frmSubscriber.email.value + '&name=' + document.frmSubscriber.name.value, true);
		// define the method to handle server responses
		xmlHttp.onreadystatechange = handleServerResponse;
		// make the server request
		xmlHttp.send(null);
	}
	else
		// if the connection is busy, try again after one second
		setTimeout('subscriber()', 1000);
}

// executed automatically when a message is received from the server
function handleServerResponse()
{
	// move forward only if the transaction has completed
	if (xmlHttp.readyState == 4)
	{
		// status of 200 indicates the transaction completed successfully
		if (xmlHttp.status == 200)
		{
			// extract the XML retrieved from the server
			txtResponse = xmlHttp.responseText;
			// obtain the document element (the root element) of the XML structure
			document.getElementById("errorMsg").innerHTML = txtResponse;
			document.frmSubscriber.name.value = '';
			document.frmSubscriber.email.value = ''
		}
		// a HTTP status different than 200 signals an error
		else
		{
			//alert("There was a problem accessing the server: " + xmlHttp.statusText);
		}
	}
}