Strategy for external javascript framework debugging

Question

Working with Extjs, GeoExt and OpenLayers, I more and more tend to run into problems which do not result in direct javascript errors (in either IE, FF or similar). It could be features not working, unexpected behaviour and so on.

My usual strategy is to strip down code to a minimum hoping to discover where the problem arises - Firebug and the IE debug tool are usually great companions. Google and various forums are always a big help – IF a similar problem has been documented by another user and IF the problem has been formulated in a way so that I find it.

But when it comes to using larger frameworks such as Extjs and OpenLayers, I find it very difficult when my debugging leads me inside the frameworks world of mysterious methods.

Asking questions here and in other forums can give fantastic results, but sometimes I cannot point to what the problem actually is – only the result I see on the screen. Using multiple frameworks it could be interference between them, unexpected behaviour when using exactly those frameworks and generally just complicating the debugging.

What do you recommend I do in these situations? What do you normally do – I would love to pick up a trick or two :)

Regards, Casper

Answer 1

I feel your pain. I use YUI a lot and sometimes errors get sucked into a bottomless pit of YUI code that doesn't generate an error per se but also doesn't do what I think it should.

In cases where I'm lucky enough that an error is thrown inside foreign code I look at Firebug's call stack and start debugging at the first place up the chain where I find my own code.

In the case of the bottomless pit swallowing errors then I resort to setting breakpoints in my code at suspicious places and single-step my way through.

Firebug is very, very useful here since it allows you to dynamically set breakpoints and conditional breakpoints. In both cases above I never reduce my problem to a minimum because the bug may be due to the complexity. Also, setting breakpoints is much easier.

About the only time I reduce my problems to a minimum is when I need to post it here or at comp.lang.javascript.

Now, if the bug only appears in IE I usually give up for the day, go home and come back tomorrow. It is a surprisingly effective strategy until my boss decides that we need to push the code to live TONIGHT (in which case I just cry inside).