What Is AJAX? How Does It Work?

AJAX stands for Asynchronous JavaScript and XML. It is used for allowing the client side of an application to communitcate with the server side of the application. Before AJAX, there was no way for the client side of a web application to communicate directly with the server. Instead, you would have to use page loads. With AJAX, the client and server can communicate freely with one another.

Here is how the usual AJAX script goes:

• Some action triggers the event, like the user clicking a button.
• The AJAX call fires, and sends a request to a server-side script, using XML
• The server-side script (PHP, ASP, or whatever) takes the input from JavaScript, can access the database if it needs to, and processes the data.
• Using XML again, the script sends the data back to the original client-side page that made the request
• A second JavaScript function, called a callback function,catches the data, and updates the web page

Throughout this tutorial, we will discuss how various scripts use this routine to accomplish a wide variety of effects.

1. Login Forms

Instead of going to a login page, and then navigating back to the page you originally wanted, with AJAX, a user can type in their user name and password directly into the original page. From there AJAX will send a request to the server to log them in. The server let’s the page know they’ve been logged in, and the page you are on can update as needed. Digg has a login-system that works like this.

Example: Digg.com (top of page)

Plugin: jQuery Form Plugin

2. Auto-Complete

Google was one of the first major companies to start using AJAX, and Google’s search suggestion tool was one of the first ways they used it, and one of the first auto-complete tools made. When typing into the Google search bar, it starts to use AJAX to get common results from the database on each keystroke. Auto-Complete is great for forms where you have a lot of possible inputs, and making a select drop down would be too long and cumbersome.

Example: Google Search

Plugin: jq autocomplete

3. Voting and Rating

Social bookmarking sites like Digg and Reddit let the users decide the main content of the site by voting on content that the users like. They use AJAX to handle all of the voting, so that the users are able to voice their opinions on a number of stories quickly and easily.

Example: Reddit

4. Updating With User Content

One of the things that made Twitter so popular was their simple and easy-to-use interface. When someone makes a ‘tweet’, it is instantly added to their feed, and everything is updated. Recently, Twitter has started using AJAX with their ‘trending topics’ pages. Every few seconds, the page lets the user know that more tweets have been made about the subject, giving them up-to-the-second updates.

Example: Twitter

5. Form Submission & Validation

Forms have always tricky to work with, but AJAX can make them a lot better for the users. AJAX can be used in a variety of ways, from the auto complete mentioned above, to validation and submission as well. Some sites use AJAX to check if a form meets certain requirements, such as password strength, or if something is a valid email or URL.

Example: 10 Cool jQuery Form Plugins

6. Chat Rooms And Instant Messaging

Chatting online has come a long way from the days of IRC. Chat rooms and instant messaging can now be handled in the browser completely. There are two main AJAX processes in a chat room or IM application. Think of one of them as your ears, and one of them as your mouth. Your ‘mouth’ updates the server and lets it know that you have sent a message. The ‘ears’ check with the server constantly, and updates your page with messages that have been sent by whoever you are chatting with.

Example: Meebo Chat (Uses Ajax)

Plugin: GMail/Facebook Style Chat Script

7. Slicker UIs

Creating a clean, slick user interface is a very popular use of AJAX. It allows users to accomplish more on a single page. The benefits of this are twofold: First, it makes using the web application quicker and easier for the user; Secondly, it cuts down on the number of requests you have to make to the server, which cuts down on bandwidth and load times. A free file upload service called Drop.io uses this well. Google has also really pushed the envelope of what is possible with AJAX by making desktop-like applications like Google Docs and Google Maps.

jQuery UI Library

8. External Widgets

When using AJAX, the page that is using the JavaScript isn’t just limited to the server it is located on. The AJAX can make a call to any server online. This is how a number of plug-ins for Content Management Systems like Wordpress work, and other various scripts like Google Adsense.

Example: Google Adsense

Plugin: Script for loading external content into div

9. Lightboxes instead of pop-ups

Pop-up blockers are very common place these days, and for a good reason: pop-ups are annoying. Using light boxes, which are pop-ups inside the browser window, the pop-up blocker can’t stop it, and they aren’t quite as irritating to the user. Some people use them for advertising, like on Darren Rowe’s ProBlogger.com. They can also be used for something like a login or register box, like Reddit does when you try to vote and you are not logged in.

Example: Logo Sauce

Plugin: Lightbox Plugin

10. Using AJAX With Flash

Using AJAX along with Flash is a rarely used technique, but it can be used to generate some impressive results. The flash game website Kongregate uses this to great effect. Using their API, they have their own achievement system that involves winning ‘badges’ for completing various accomplishments in games. When a badge is earned, the API in Flash sends a response back to JavaScript, which then uses AJAX to update the user’s profile with the newly earned award.

Example: Kongregate

Plugin: jQuery Flash Plugin

I hope this article has given you a lot of ideas of how you can use AJAX to improve and expand your web applications. What are some other uses you can think of for AJAX?

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