Test Page

Some call it JSONP , others On Demand Javascript

Version B

This is a slightly improved version of this page.
Additional feature: It uses event handlers to detect a failure earlier (case 3 and 4). Different events need to be checked in IE vs. the rest.
The returned data looks like: myData = { ... } Details in the box below.
Successfully tested in: IE7, FF3, Chrome.
Check out also these versions:
- Version A - returned data looks like myData = { ... }, uses a repeated timer to detect data arrival and failure.
- Version C - returned data looks like processData({ ... }), uses a callback function and a single time to detect a failue.

Klick to load data - case 1a: should work just fine, immediate response
the request includes a bogus parameter to make sure the data is not loaded from the browser cache

Klick to load data - case 1b: should work just fine, immediate response
without a bogus parameter, so the data might come from the browser cache (depending on your browser and its settings)

Klick to load data - case 2a: simulates a slow response, it takes about 10 seconds for the data to arrive, whereas the timeout is chosen to be 5 seconds
the request includes a bogus parameter to make sure the data is not loaded from the browser cache

Klick to load data - case 2b: simulates a slow response, it takes about 10 seconds for the data to arrive, whereas the timeout is chosen to be 5 seconds
without a bogus parameter, so the data might come from the browser cache (depending on your browser and its settings)

Klick to load data - case 3: simulates an internal server error (error 500)

Klick to load data - case 4: simulates server down / not reachable

the returned data

room for state changes, the current state is displayed · see source code · clear

room for error message

Recommendation:

In the usual case of no error version C with the callback function is the fastest, since the data is processed immediately when it arrives. Version A and B are not much slower, but need the additional overhead of a repeated timer.

In the case of failure, version B is the fastest by far. The failure is picked up by the event handlers, where the other versions just sit and wait until some time limit is up and then check if the data arrived correctly. However, different browsers use different event handlers, so extra work has to be done. Opera 9.6 does not seem to fire the onerror event correctly (Version B, case 3 and 4). But no harm is done, the timeout catches the failure at last.

Conclusion: The differences are small. If everything works as expected all versions seem reasonable. That said, if browser compatibilty is most important to you, use version C. Otherwise go with version B.

Comment are welcome and might appear here after a while unless you wish otherwise (sorry my page is not set up to do this automatically).