Google Closure: Centralized AJAX 'decoder'?

Question

First of all, I must say that I'm very new to Google Closure, but I'm learning :)

Okay, so I'm making a web app that's going to be pretty big, and I thought it would be good to manage all the AJAX requests in one XhrManager. No problem there.

But, is it possible to have some kind of default callback that would check for errors first, display them if necessary and then when it passes, launch the "real" callback? I'm talking about a feature like the decoders in amplify.js . Here's their explanation:

Decoders allow you to parse an ajax response before calling the success or error callback. This allows you to return data marked with a status and react accordingly. This also allows you to manipulate the data any way you want before passing the data along to the callback.

I know it sounds complicated (and it is, really), so the fact that I'm not that good at explaining helps a good deal too, but yeah.

The solution I have in my head right now is creating an object that stores all the 'real callbacks', of which the 'error-checking callback' would execute the correct one after it finished checking, but I feel that's a bit hack-ish and I think there has to be a better way for this.

Answer 1

Since you always have to decode/verify your AJAX data (you never trust data returned from a server now do you?), you're always going to have different decoders/verifiers for different types of AJAX payloads. Thus you probably should be passing the decoder/verifier routine as the AJAX callback itself -- for verifications common to all data types, call a common function inside the callback.

An added benefit of this will be the ability to "translate" unmangled JSON objects into "mangled" JSON objects so that you don't have to do use quoted property access in your code.

For example, assume that your AJAX payload consists of the following JSON object:

{ "hello":"world" }

If you want to refer to the hello property in your code and still pass the Compiler's Advanced Mode, you'll need to do obj["hello"] . However, if you pass in your decoder as the callback, and the first line you do:

var decoded = { hello:response["hello"] };

then do your error checking etc. before returning decoded as the AJAX response. In your code, you can simply do obj.hello and everything will be nicely optimized and mangled by Advanced Mode.