PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Fundamental Ajax
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function getServerTime() {
var thePage = 'servertime.php';
myRand = parseInt(Math.random()*999999999999999);
var theURL = thePage +"?rand="+myRand;
myReq.open("GET", theURL, true);
myReq.onreadystatechange = theHTTPResponse;
myReq.send(null);
}
The first line in the function creates a variable called thePage with a value of servertime.php.This
is the name of the PHP script that will reside on your server.
The next line may seem out of place, as it creates a random number.The obvious
question is “What does a random number have to do with getting the server time?”The
answer is that it doesn’t have any direct effect on the script itself.The reason the random
number is created, and then appended to the URL in the third line of the function, is to
avoid any problems with the browser (or a proxy) caching the request. If the URL were
simply http://yourserver/yourscript.php, the results might be cached. However, if the
URL is http://yourserver/yourscript.php?rand=randval, there isn’t anything to cache
because the URL will be different every time, although the functionality of the underlying
script will not change.
The final three lines of the function use three methods (open, onreadystatechange,
and send) of the instance of the XMLHTTPRequest object created by calling
getXMLHTTPRequest() as seen in the previous section.
In the line using the open method, the parameters are the type of request (GET), the
URL (theURL), and a value of true indicating that the request is to be asynchronous.
In the line using the onreadystatechange method, the function will invoke a new
function, theHTTPResponse, when the state of the object changes.
In the line using the send method, the function sends NULL content to the server-side
script.
At this point, create a file called servertime.php containing the code in Listing 34.1.
Listing 34.1
The Contents of servertime.php
This script gets the current server time, through the use of the date() function in PHP,
and returns this value within an XML-encoded string. Specifically, the date() function
is called twice; once as date('H:i:s'), which returns the hours, minutes, and seconds of