What Is Ajax?
Ajax is a group of programming techniques that enable update of a web page or taking some information from server without page refresh. Web browser still connects to web server, but web application is more interactive because usually only small amount of data is updated.
Ajax is acronym for Asynchronous JavaScript And XML. Its full name tells us a lot about how Ajax works and which technologies are used.
So, Ajax enabled web application can make asynchronous call to web server by using a JavaScript. Note that asynchronous call can be made by any client side script language, not only JavaScript. For example, VbScript is also capable for this, but it is not supported by many web browsers.
Also, data are usually retrieved in form of XML, but web server output can be in any form, including plain text. Most popular alternative to XML is JSON (JavaScript Object Notation).
Advantages of Ajax
Using of Ajax can make your web application more interactive, faster and remove page refresh (page refresh is often annoying issue in chat application). Web application can request only content that is changed, instead of complete page.
Disadvantages of Ajax
- Ajax pages usually are not indexed well by search engines, because search engines have a problem with JavaScript.
- Pages created dynamically are not visible in browser's history.
- Some browsers don't support JavaScript and even if browser support JavaScript, visitor is maybe disabled it.
- Some mobile phones and PDA's don't support JavaScript.
- Possible security problem. You need to take care of every user request, manage state, check user input etc.
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