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

Answer 1

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.