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As many of us already know, the secret ingredient of Ajax is the XMLHttpRequest JavaScript Object which allows asynchronous requests for data to the server and updates the web page without doing a full page reload.
In a nutshell, JavaScript client code manipulates the Document Object Model (DOM) of the web page using XMLHttpRequest and callbacks to send and receive data asynchronously.
With Ajax you can decide to move all the presentation layer to the client side.
Improving But, improving UX could also imply more complex GUI and a lot more work for developers. The challenge is to keep happy users, developers and software architects as well