The internet wasn't made for this. The web browser closes connection with web server as soon as it has received all data. This means that after this no more data can be exchanged. What if you want to do an update though? If you're building a PHP application (e.g. a high-quality content management system), then it'd be ideal if it worked almost like a native Windows/Linux application.

But that requires real-time updates. Something that isn't possible, or so you would think. A good example of an application that works in (almost) real-time is Google's GMail. Everything is JavaScript powered, and it's very powerful and dynamic. In fact, this is one of biggest selling-points of GMail. What if you could have this in your own PHP websites as well? Guess what, I'm going to show you in this article.

How does it work? If you want to execute a PHP script, you need to reload a page, submit a form, or something similar. Basically, a new connection to server needs to be opened, and this means that browser goes to a new page, losing previous page. For a long while now, web developers have been using tricks to get around this, like using a 1x1 iframe, where a new PHP page is loaded, but this is far from ideal.

Now, there is a new way of executing a PHP script without having to reload page. The basis behind this new way is a JavaScript component called XML HTTP Request Object. See http://jibbering.com/2002/4/httprequest.html for more information about component. It is supported in all major browsers (Internet Explorer 5.5+, Safari, Mozilla/Firefox and Opera 7.6+).

With this object and some custom JavaScript functions, you can create some rather impressive PHP applications. Let's look at a first example, which dynamically updates date/time.

Example 1 First, copy code below and save it in a file called 'script.js':

 var xmlhttp=false; /*@cc_on @*/ /*@if (@_jscript_version >= 5) // JScript gives us Conditional compilation, we can cope with old IE versions. // and security blocked creation of objects.  try {  xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");  } catch (e) {  try {  xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");  } catch (E) {  xmlhttp = false;  }  } @end @*/ if (!xmlhttp && typeof XMLHttpRequest!='undefined') {  xmlhttp = new XMLHttpRequest(); }
function loadFragmentInToElement(fragment_url, element_id) {  var element = document.getElementById(element_id);  element.innerHTML = '<em>Loading ...</em>';  xmlhttp.open("GET", fragment_url);  xmlhttp.onreadystatechange = function() {  if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {  element.innerHTML = xmlhttp.responseText;  }  }  xmlhttp.send(null); } 

 <?php echo date("l dS of F Y h:i:s A"); ?> 

Cookies in a nutshell Cookies are small pieces of information that is stored on computer of your visitors. Each browser handles it differently, but most simply store information in a small text file. Internet Explorer has a special folder, which can be found in your C:Windows or C:WindowsSystem32 folder. You can delete all your cookies, by going to Options and 'Clearing Cookies' or deleting them by hand. I don't recommend this though.

Almost every website uses cookies. If you go to Amazon.com, you will get several cookies. The same goes for CNN.com. Even Google uses cookies! They are extremely useful for (temporarily) storing information. For example, if you have a login system for your visitors, you could save their userid and password (very heavily encrypted!) so they are automatically logged in next time they visit your website.

Or you could remember their last visit, and highlight everything that is new. And that's just beginning.

Using Cookies Using cookies in PHP is extremely easy. In fact, there is nothing to it, because of PHP's inbuilt setcookie() function. Have a look at documentation, and then try following example:

<?php

// Set a cookie // Cookie name: name // Cookie value: Dennis Pallett // Cookie expire: in 24 hours

setcookie ('name', 'Dennis Pallett', time() + (60*60*24)); ?>

If you run code above, then a cookie will be set. That's all. The cookie name and value are pretty obvious. The cookie expire is when cookie expires, or goes away. Simply use time() function and add number of seconds you want to have cookie available to it. In example I added 60*60*24=86400 seconds, or 24 hours.

If you have looked at documentation, you probably noticed there are additional arguments. As documentation says, path is to limit a cookie to a specific path on your web server. This is often used when you run multiple instances of same script in separate directories. You can safely omit this argument when it doesn't matter if cookie is available site-wide.

There is also domain argument. This can be used to limit cookie to a specific sub-domain, e.g. test.example.com. You can also safely ignore this argument, or set it to .example.com (note beginning period, this is essential!).

Finally, there is also secure argument. This argument is only used for cookies that are sent over a secure HTTPS connection (SSL). Just ignore this argument, unless you're working with a secure connection.

One thing that should be mentioned is that cookies must be set, before you display any HTML/text. It's probably best if you turn on output buffering by putting ob_start() at top of your page.

Now that you have set a cookie, you probably want to retrieve value as well. After all, that is whole point of using cookies. Thankfully, as PHP is ever so easy, you can retrieve same way as you retrieve a GET value. See following example to retrieve value of previous example:

<?php echo 'Your name is ' . $_COOKIE['name']; ?>

This should print "Your name is Dennis Pallett". There's nothing more to it. It's just that easy!