AJAX - what it is and other definitions

AJAX stands for Asynchronous Javascript and XML.

It involves several components including:

1. DOM - Document Object Model. This is on the client side and is modified by JavaScript to dynamically change what the users sees.
2. XMLHttpRequest - this send and receives data to/from the server in the background. This does not require the page to be reloaded as is the case with the traditional HTML Post method.
3. XML - or other format, for sending data back to server. It does not have to be XML format.

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Mashup - Combine output from several sites - using their APIs
JavaScript - the only script supported by all the major browers. IE, Firefox, Opera, Safari. There are cicumstances where it may not be supported, for example, the user may have disabled JavaScript in their brower, or they could be using a mobile phone.