What data formats can AJAX transfer?

Question

I'm new to AJAX, but as an overview I'd like to know what formats you can upload and download. Is it limited to JSON or XML or can you even send binary types like MP3 or UTF-8 HTML. And finally, do you have full control over the data, byte for byte in something like a byte array, or is only a string sent/received.

Answer 1

There is a Digg the Blog entry titled DUI.Stream and MXHR that shows off what they call "Multipart XMLHttpRequests." It is alpha code now, but there is a demo that handles images.

Answer 2

If we are talking about ajax we are talking about javascript? And about XMLHTTPRequest?

The XMLHttpRequest which is only a http request can transfer everything. But there is no byte array in javascript. Only strings, numbers and such. Every thing you get from an ajax call is a piece of text (responseText). That might be parsed into XML (which gives you reponseXML). Special encodings should be more a matter of the http transport.

The binary stuff is not ajax dependent but javascript dependent. There are some weird encodings for strings to deliver byte data inside in javascript (especially for images) but it is not a general solution.

HTML is not a problem and that is the most prominent use case. From this type of request you get an HTML string delivered and that is added to some node in the DOM per innerHTML that parses the HTML.

Answer 3

You can transfer any type of data either string or bytes

Answer 4

AJAX simply means you're transferring data asynchronously over HTTP with a JavaScript call. So your script makes a "normal" HTTP request using the XmlHttpRequest() object. However, as the name implies, it's really only suited for text-based data formats since you generally want to perform some action on the client side with the data you got back from the server (not always though, sometimes people just send XmlHttpRequests only to update something on the server).

On a side note, I have never seen an application where sending binary data would have been appropriate anyway.

Most often, people choose to send data over to the server with POST or GET (which is basically a method to transfer name-value pairs inherent to HTTP). For sending more complex data, for example hierarchical structures, they need to be encoded somehow. XML documents can be made natively per JavaScript, sent over to the server and get parsed into whatever data types necessary. But since XML can be a bit of a pain, many devs use JSON encoded data instead because it's easy to generate and easy to parse.

What the server sends back is equally as arbitrary. Usually, you specify a callback function in your Javascript that handles the incoming data. Again, the popular choices are XML and JSON, they parse easily into a document object or an array structure respectively. You could also send plain text or some other packaging but remember that you then have to take care of extracting the usable data from it yourself. Sometimes, it can also be beneficial to send actual HTML fragments to the client to update something on the page directly.

For starters, I suggest you have a look at JQuery. It's a very lightweight framework that abstracts many of evil compatibility stuff and lets you write AJAX requests very nicely.

Answer 5

Since data is transported via HTTP you will have to make sure that you use some kind of encoding. One of the most popular is base64 encoding. You can find more information at: http://www.webtoolkit.info/javascript-base64.html

The methodology is to base64-encode the data you would like to send and then base64-decode the data at the server(or the client) and use the original data as you intended.

Answer 6

You can move anything that can be sent over HTTP. There are restrictions about the call being made to the same domain as the page loaded from, but not on the content of the transfer. You can do either GET or POST transactions too.