var xmlHttpVariable; // Declare a global variable.

// HTTP request object.
function GetXmlHttpObject()
{
    var xmlHttp = null;

    try
        {xmlHttp = new XMLHttpRequest();}
    catch (e)
    {
        try
            {xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");}
        catch (e)
            {xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");}
    }

    return xmlHttp;
}

function callServer()
{
    xmlHttpVariable = new GetXmlHttpObject(); // Call HTTP request object.
    var url = "url"; // Set the URL to the server-side script.
    var variables = "var1=val1&var2=val2"; // Set the variables.
    xmlHttpVariable.onreadystatechange = stateChangedVariable; // Call a function on state change.
    xmlHttpVariable.open("POST",url,true); // Open the URL.
    // Send the proper header information along with the request.
    xmlHttpVariable.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xmlHttpVariable.setRequestHeader("Content-length", variables.length);
    xmlHttpVariable.setRequestHeader("Connection", "close");
    xmlHttpVariable.send(variables); // Send the variables.
}

function stateChangedVariable()
{
    if (xmlHttpVariable.readyState == 4) // Values for readyState see below for explanations.
    {
        if (xmlHttpVariable.responseText.replace(/^\s+|\s+$/g, ”) == ‘return value’)
            {// Action here.}
    }
}