Dec 24

what is ajax in asp.net


When you want a user to send data to your server — once they have filled out a form, for example — they normally have to submit the form and then wait as the entire page is refreshed. Similarly, if you want to retrieve new data from the server, you have no choice but to load a whole new page.

This is inefficient, time-consuming, and particularly frustrating if there’s only a small amount of data being sent back and forth. In this tutorial, you’ll be introduced to Ajax, a technology that allows you to send these requests through small JavaScript calls, meaning the user doesn’t have to wait for the page to refresh.

What is “Ajax”?

Ajax is actually a family of technologies that have been available for years. The means to make requests to the server using only JavaScript were built into Internet Explorer 5.5, but the possibilities of the technology were overlooked. It was only in 2005 that the techniques were rediscovered and used, notably to excellent effect in Google’s .

The term Ajax, which stands for “Asynchronous JavaScript and XML”, was first coined by Jesse James Garrett in his somewhat infamous article,

So let’s take each of those parts in isolation. Ajax is:

This means that when you send a request, you wait for the response to come back, but are free to do other things while you wait. The response probably won’t come back immediately, so you set up a function that will wait for the response to be sent back by the server, and react to it once that happens.
JavaScript is used to make a request to the server. Once the response is returned by the server, you will generally use some more JavaScript to modify the current page’s document object model in some way to show the user that the submission went through successfully.
The data that you receive back from the server will often be packaged up as a snippet of XML, so that it can be easily processed with JavaScript. This data can be anything you want, and as long as you want.

There’s nothing really new about what is happening here. We’re requesting a file (which will often be a serverside script, coded in something like PHP), and receiving a page as the response. This is how the web works already — the only difference is that now we can make these requests from JavaScript.

Cross-browser Ajax

Unfortunately Ajax is supported slightly differently in IE than it is Safari, Opera and Mozilla-based browsers like Firefox. This leaves us with two possible routes: using code branching to send the right code to each browser based on which model they support, or using a JavaScript library that wraps up the Ajax code into a single object, and means you don’t have to worry about browser incompatibilities.

We’re going for the latter option, and will be using a JavaScript library. There are dozens of them in existence, each with their own boons and vices. Popular examples include prototype, Dojo, and the Yahoo UI library. For the duration of this tutorial, we’re going to be using a very useful library called » Sarissa. Sarissa contains methods that will create the request for us, and also methods that help with processing the XML that we receive back in the response. This means we don’t have to mess with the intricacies of Ajax, and allows our code to be quite elegant.

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