What is AJAX ?

AJAX is just an acronym refering to Asynchronous JAvaScript and XML.

Its a technique for creating fast and dynamic web pages.

 AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.Classic web pages, (which do not use AJAX) must reload the entire page if the content should change.

Examples of applications using AJAX: Google Maps, Gmail, Youtube, and Facebook tabs. Now, if we take a look at the words Asynchronous JAvaScript and XML, most of us know what JavaScript and XML are, but the term Asynchronous can be confusing, so let’s focus on that.

What does asynchronous refer to?

Asynchronous refers to events that are happening on the background independently of the main application flow. These events do not disturb the flow of the application, allowing the continuation of it’s normal process.

 A fairly good example of this happening is in your Facebook home page, when all of a sudden, without refreshing your browser window, you notice that there are new status feed updates from your friends. ( Although I did notice, and think many have as well, how they do implement this. If you haven’t then, try leaving your facebook homepage on the browser without moving your mouse for about 1 minute. After that minute, just move your mouse from one point to another, and all of a sudden, you will see the feeds get updated. )

 I’m assuming they are using some jQuery mousemove or something similar for this to happen. So what happens there is, facebook sends your profile information ( or your user id ) to their servers. Their servers then look for your friends list, grab their newly added status, return the result to the browser and then add them to your wall so that you can see. All of that, without pressing that refresh button.

So you see, AJAX allos you to update a web page asynchronously on the background by exchanging simple, and small amounts of data. Some more examples of pages using AJAX is: Youtube, Gmail, Google Maps, StackOverflow and many more on the web.

So you are still asking yourself, What is AJAX? Well, I’m going to ask for forgiveness, as I have no art skills, but the following image should help you just a little bit.

Some advantages

AJAX, you see, is based on internet standards. It uses a combination of the following to accomplish it’s goal:

• XMLHttpRequest Object(Modern Broswers and IE7+)
• ActiveXObject (IE6 and below)
• JavaScript/DOM (Used to interact browser and server)
• XML (Returned results)
• JSON (Returned results)
• HTML (Returned results)

These standards are browser based, making them platform independent. It doesn’t matter where you program this in, as long as you have a browser, then this ‘should’ work. All you would need is a server with the application files, and the browser should do the rest.

Another advantage using AJAX would be a better user interactivity. This could be named the most obvious benefit of using AJAX, and why web developers and webmasters are using AJAX more and more every day. AJAX simplifies the flow of an application, thus making it have quicker interaction between user and website since pages are not reloaded for content to be displayed. This activity can be simplified, since the loading times can be reduced from websites.

The advantage above opens up for this next advantage, which you can call it, smoother navigation on a website. While using AJAX, users will not have the need to use the refresh nor the back button, thus, allowing quicker response from the server.

Some Disadvantages

Everything that has an advantage, will most likely have disadvantages, and AJAX surely has some that I will mention.

Even though the back and refresh button are not needed while navigating a website with AJAX, these two buttons can become useless. This is due to the fact that, AJAX ‘navigating’ does not change you URL, so if you were in the middle of a process, and have no direct URL to where you were, then this might be bad. In some cases, the use of Hijaxing is used, which is the use of hashing url (#) at the end.

Another disadvantage would be that it is dependant on JavaScript. While it is ok to depend on it, since most modern (if not all) already use it, but in some cases, there are users who prefer disabling JavaScript. This makes AJAX worthless. Gladly, there is a workaround this problem, as web developers must have in mind, every time they create an AJAX Website, they need to always think of this and make an optional non-AJAX version of the AJAXified website they just created.

The last disadvantage I want to point out would be the SEO factor. Since there are no SEO Friendly URL’s, then search engine tend to bypass your application, and it would appear as if that part of your site does not exist.