Ajax

The World Wide Web Consortium (W3C) has begun standardizing AJAX technology, which is gaining in popularity among web programmers.

Ajax is based on two basic principles:

• Use DHTML to dynamically change the content of a page.
• Using the technology of dynamic access to the server "on the fly", without reloading the entire page completely, for example:
  • using XMLhttpRequest,
  • through the dynamic creation of child frames,
  • via dynamic JavaScript creation with the loading of the script body.

By and large, how does the software on your desktop differ from online web applications? Greater saturation with interactive elements and the time of their reaction are the main problems that increase the distance between web interfaces and their users. But this distance began to decline.

You are already familiar with new items like Google Suggest, Google Maps? Probably came across to you and LiveSearch (Search live) on some blogs of their advanced owners? All this is now referred to as Ajax (technically - XMLhttpRequest).

What is Ajax?

If we talk about the nearest technological future of the Web, then probably Ajax (Ajax) can be called one of the most real and expected evolutionary steps.

In fact, Ajax is not a technology, but a sum of them, where each term develops in its self-sufficiency and blends together with the rest of the terms into something new and extremely powerful.

Among the main components of Ajax are the following:

• Compatible with Web standards for reporting data using XHTML and CSS.
• Dynamic mapping and interaction with these data using the Document Object Model.
• Data exchange and data manipulation using XML and XLST.
• Asynchronous data retrieval using XMLhttpRequest.
• JavaScript as the language of the binder is all of the above.

How does Ajax work?

The essence of Ajax methodology is to minimize the cycle of "data transmission/pause, waiting for an answer" and try to make the user's communication with a particular website as even as possible.

Ajax is like a layer between the user and the server, usually loaded first in a hidden frame, and which makes sure that the data is loaded only when necessary and only those that are needed.

All user requests, usually sent to the web server, are instead routed to the Ajax engine through a special JavaScript code. The engine decides whether it is necessary to download data from the server or not. If the data needs to be sent or downloaded, this happens against the background and regardless of the web application itself, without interrupting the process of the user communicating with the website. Data is sent and received asynchronously, usually using an XML representation.

By and large, the heart of Ajax technology is XMLhttpRequest, a JavaScript object that allows you to perform further requests to the server after the page has already loaded.

However, it is not very convenient to use the name "X-em-el-ash-ti-pi-riqvest" and Jesse James Garrett from AdaptivePath suggested to name this set of technology - Ajax (Asynchronous JavaScript + XML). Simply and sonorous.

Although it will not be long before the technology rolls through and becomes available to a wide range of developers, in the near future, I enthusiastically await the emergence of new Ajax-based websites. I'm very interested in where I can get authors who are not afraid of experiments, creative approach.

In fact, we are waiting for something really new in the site construction, an evolution that will set new standards for web development.

Disadvantages

In AJAX itself there are no minuses either, as there is nothing wrong with sugar. All negative comes from excessive use or use.
You've probably met more than once with pages overloaded with JavaScript.
All should be where you need and no more than necessary. Who does not like pages that quickly load?

For example, I'm not a cameraman, but I correctly distinguish the work of a bad operator from good. If we constantly want to take a closer look or wait for the camera to turn and show what is on the left. Hence, the operator is bad. And when they forgot about him, then we deal with the professional.
AJAX should be used so that it is not noticed.

Saving pages

Far not always created using Ajax page can be saved on disk, but sometime it is necessary.

Registration in search engines

Unfortunately, search engines crawl the source code, not the result. Because many materials become unavailable.

References

Submit a page that displays a list of cities with the possibility of filtering through the selection of the country in the selection list. Many sites now do this through Ajax and similar technologies, redrawing the list without changing the address of the page. It is terribly inconvenient for the user, because There is no way in this case to keep the address of the page with the already chosen country choice in the chosen address.