Today I finished a small django middleware that facilitates development of AJAX applications. I reckon most if not all Django developers know about Django’s useful debug-mode unhandled error page (you know, the one that looks like this). However, when an AJAX request reaches a faulty view, the error page will not be rendered in your browser but instead be received by your AJAX error handler (assuming you even had one), which is almost always not what you want. This forces you you to find some other way to reach your traceback information. For example, before I wrote this package, I used to regularly open Chrome’s developer tools, find the failed resource in the Resources tab, and then either read through the raw HTML (yuck) or copy and paste it to a file and double click it (tedious).
As you can see, this bothered other people, too, but I couldn’t find a decent solution on the web. Thankfully, since the problem is really about ease of development and not very relevant in environments where DEBUG is false (you’d get the traceback via email anyway), and since I do most of my development work locally (and I suspect so do many other Django developers), I figured the solution can take advantage of the server being a full fledged desktop with a modern browser and a GUI. Enter ajaxerrors.middleware.ShowAJAXErrors.
This little middleware intercepts all unhandled view exceptions, pickles the technical error page and uses Python’s webbrowser module to direct a new browser tab at a special URL that will serve (and delete) the previously stored page. All this is only triggered if DEBUG and request.is_ajax() is true, so pretty much everything you’re used to in your development flow should stay the same. Sweet. ShowAJAXError can also be configured to run arbitrary user-defined handlers with the error information, and even comes with a handler for growlnotify and a handler that replies to all failed AJAX calls with HTTP OK result containing an empty JSON object (I use it for development, YMMV).
django-ajaxerrors is on PyPI, so you can install it with pip or easy_install with ease. You can clone/fork the code (and read the more detailed readme) here. Also, if you’d like to see what django-ajaxerrors is like without any special effort, you can download a simple AJAX app I’ve written for the purpose of developing django-ajaxerrors itself. The app has django-ajaxerrors contained within it, so this is pretty much all you need to see django-ajaxerrors in action about 1 minute from now:
[sourcecode language=”bash”]
$ virtualenv -q demo
$ pip install -q -E demo django
$ cd demo
$ source bin/activate
(demo)$ curl -s -o – http://cloud.github.com/downloads/yaniv-aknin/django-ajaxerrors/ajaxerrors-demo.tar.bz2 | tar jx
(demo)$ cd ajaxerrors-demo/
(demo)$ python manage.py runserver
# demoserver running…
[/sourcecode]
Now point your browser at the development server, and play with the calculator a bit. Hint: the calculator is not protected against division by zero. 🙂
I hope you like django-ajaxerrors, it’s MIT licensed, so do what you will with it. Let me know if you need assistance or ran into a snag, or, even better, if you want to contribute something to it.
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