With few lines of JavaScript and CSS you can make a simple AJAX progress bar. JavaScript will periodically ask for progress value and server will respond with XML. Progress value should be extracted from the XML and displayed as width of the DIV element. To start progress bar in this example, please click on the Start button and wait for a second to begin. If you have installed Firebug, open Net tab and watch how this page sends request to the Web server.
More precisely, every 1000ms send_request() function sends request to the server (see setInterval line in polling_start() function). ajax-progress-bar.php returns XML and request_handler() processes received XML. Progress value from XML has meaning of percentage completion of a job.
In the following JavaScript source, please focus to the sending and handling requests. Initialization of the XMLHttpRequest is written in the cross-browser manner and there's nothing more to add. The onreadystatechange property is a function that receives the feedback. It is important to note that the feedback function must be assigned before each send, because upon request completion the onreadystatechange property is reset. This is evident in the Mozilla and Firefox source.
// create XMLHttp request object in a cross-browser manner
initXMLHttpClient = function () {
var XMLHTTP_IDS,
xmlhttp,
success = false,
i;
// Mozilla/Chrome/Safari/IE7+ (normal browsers)
try {
xmlhttp = new XMLHttpRequest();
}
// IE(?!)
catch (e1) {
XMLHTTP_IDS = [ 'MSXML2.XMLHTTP.5.0', 'MSXML2.XMLHTTP.4.0',
'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP', 'Microsoft.XMLHTTP' ];
for (i = 0; i < XMLHTTP_IDS.length && !success; i++) {
try {
success = true;
xmlhttp = new ActiveXObject(XMLHTTP_IDS[i]);
}
catch (e2) {}
}
if (!success) {
throw new Error('Unable to create XMLHttpRequest!');
}
}
return xmlhttp;
};
// send request to the server
send_request = function () {
if (number < number_max) {
request.open('GET', 'ajax-progress-bar.php', true); // open asynchronus request
request.onreadystatechange = request_handler; // set request handler
request.send(null); // send request
number++; // increase counter
}
else {
polling_stop();
}
};
// request handler (started from send_request)
request_handler = function () {
var level;
if (request.readyState === 4) { // if state = 4 (operation is completed)
if (request.status === 200) { // and the HTTP status is OK
// get progress from the XML node and set progress bar width and innerHTML
level = request.responseXML.getElementsByTagName('PROGRESS')[0].firstChild;
progress.style.width = progress.innerHTML = level.nodeValue + '%';
}
else { // if request status is not OK
progress.style.width = '100%';
progress.innerHTML = 'Error:[' + request.status + ']' + request.statusText;
}
}
};
// button start
polling_start = function () {
if (!intervalID) {
// set initial value for current number of requests
number = 0;
// start polling
intervalID = window.setInterval('send_request()', 1000);
}
};
// button stop
polling_stop = function () {
// abort current request if status is 1, 2, 3
// 0: request not initialized
// 1: server connection established
// 2: request received
// 3: processing request
// 4: request finished and response is ready
if (0 < request.readyState && request.readyState < 4) {
request.abort();
}
window.clearInterval(intervalID);
intervalID = false;
// display 'Demo stopped'
progress.style.width = '100%';
progress.innerHTML = 'Demo stopped';
};
Here you can see the source of ajax-progress-bar.php (how is job progress emulated). In your case you will have to calculate percentage of completion and return it in XML format. Caching for ajax-progress-bar.php should be disabled. Many proxies and clients can be forced to disable caching with "header" lines pragma, cache-control and expires.
<?php
// no cache
header('Pragma: no-cache');
// HTTP/1.1
header('Cache-Control: no-cache, must-revalidate');
// date in the past
header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');
// define XML content type
header('Content-type: text/xml');
// print XML header
print '<?xml version="1.0"?>';
// prepare demo progress value
$progress = (mktime() % 50) * 2;
?>
<DOCUMENT><PROGRESS><?php print $progress ?></PROGRESS></DOCUMENT>
Download source code: redips6.tar.gz
11/21/2010 - Code tested with JSLint & enabled source download
06/10/2011 - Added limit of how many times to request the server (automatic demo stop)
Impressive article ...
Why XML? Couldn't you have returned the number in plain text instead?
Yes, ajax-progress-bar.php could have only one line < ?= mktime() % 100 ?> and in this case progress value should be taken with responseText method (instead of responseXML). Hmm, but then the post should be called "AJA progress bar".
I'm just kidding, I wanted to show how is easy to create the XML communication between client JavaScript and PHP backend. This way you can extend XML and send even more data if you want instead of progress value only.
Nice article.
But I have a question: is it possible to stop sending requests when the progress bar has reached 100%?
Thanks in advance!
I've found the solution myself (maybe I can help some people with it):
In request_handler, I check if the progress >= 100, if it is so, I call the function polling_stop().
Your content is awesome. Thanks for the code.
I have want to use your progress bar in my web application. And im using JSP as my client side. How can i generate XML from my JSP. and instead of using mktime() method what should i use. Thanks in advance
Noel,
I suppose that the simplest way to create XML from the JSP page is with out.println (JSP experts, please correct me). This page is only demo and shows how to display work progress. In your case (instead of mktime) you will have to build some logic in JSP and return percentage of job done.
Thank you so much,it's a very helpful example.
i made a large mysql insert query (500,000+ insert lines) and i want to show the users how far they've gone.
is it possible to get the current insert point while the insert page is still loading?
Thats a very impressive article. But, how do I implement the same in Asp.net? Can U help me out for this?
@Wilson - I suppose if you have insert in loop, then you can increase progress value after let's say every 5000 inserts. This progress value should be read in ajax-progress-bar.php. Or just read count(*) of inserted rows, but I'm not sure if MySQL could respond fast with counted rows while inserting at the same time.
@Ronny - I'm sorry but ASP.NET is not in list of my technologies. Anyway, your main task will be to customize ajax-progress-bar.php to become ajax-progress-bar.aspx (that means to create simple code to output XML). In send_request() function, you will have to rename function call also. I hope that somebody familiar with ASP.NET will help you more.
Great article. But how exactly do you embed that to html code. Say I want to execute a command on the server on the click of a button on the page which javascript function do I need to run. Can you please help. Many thanks!
What does ajax-progress-bar.php do?
This is not working under IE6... can anyone help me?
@Mark - Please see the request_handler() function. After browser got reply from the server, element width changes according to the PROGRESS value in XML. To execute command on the server on the button click, you can use classic post-back approach or you can try with AJAX. AJAX can send request to the server in "background", so the current page will not refresh. To start with AJAX, you can use initXMLHttpClient(), send_request() and request_handler() functions. Please do not forget to initialize XMLHttpClient object before sending request.
In this example, ajax-progress-bar.php emulates progress of some server work. Actually, it only generates XML with progress value.
@Janki - Demo in this post should work in IE6. I test it with IETester and it works. Please try to click on the button "Start" and wait few seconds. Progress bar should grow every 1.5 seconds.
Pingback: Simple AJAX progress bar | Ajaxmint - Endless Ajax samples on jQuery, MooTools, ExtJS, Dojo, Prototype and PHP
Hi,
what does your ajax-progress-bar.php do?
@Nick - ajax-progress-bar.php emulates some job progress. Actually it calculates percentage based on current time for this demo. Simply enough to show a communication between server side and AJAX JavaScript.
I'm an AJAX newb but I think I get most of this.
I'm just finding the mechanism by which you time a process a little vague.
If ajax-progress-bar.php was just
<?php
$y=0;
for($x=0;$x
at what point and how would I enable the above to send anything meaningful to your javascript code?
Thanks for any clarification,
R