AJAX and PHP

Server-Side Techniques with PHP and MySQL
Server, gimme some random numbers!
3. In the same folder, create smartproxyping.js:
// holds an instance of XMLHttpRequest
var xmlHttp = createXmlHttpRequestObject();
// holds the remote server address and parameters
var serverAddress = "smartproxyping.php";
var getNumberParams = "action=GetNumber" + // get a new random number
"&min=1" + // the min number to generate
"&max=100"; // the max number to generate
var checkAvailabilityParams = "action=CheckAvailability";
// variables used to check for server availability
var requestsCounter = 0; // counts how many numbers have been retrieved
var checkInterval = 10; // counts interval for checking server
availability
var updateInterval = 1; // how many seconds to wait to get a new number
var updateIntervalIfServerBusy = 10; // seconds to wait when server busy
var minServerBufferLevel = 50; // what buffer level is considered acceptable
// creates an XMLHttpRequest instance
function createXmlHttpRequestObject()
{
// will store the reference to the XMLHttpRequest object
var xmlHttp;
// this should work for all browsers except IE6 and older
try
{
// try to create XMLHttpRequest object
xmlHttp = new XMLHttpRequest();
}
catch(e)
{
// assume IE6 or older
var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
"MSXML2.XMLHTTP.5.0",
"MSXML2.XMLHTTP.4.0",
"MSXML2.XMLHTTP.3.0",
"MSXML2.XMLHTTP",
"Microsoft.XMLHTTP");
// try every prog id until one works
for (var i=0; i