Question

46

Break on a change of variable value

rated 0 times [ 52] [ 6] / answers: 1 / hits: 36476 / 13 Years ago, thu, october 27, 2011, 12:00:00

Similar to other questions here, like this one.

Is there a way to break on the change of a variable value in any JavaScript debugger? (like IE Developer tools, Visual Studio, or Firebug)?

I guess it's something like a watch variable, but I want to be able to see the callstack and pause it when the change to the variable actually occurs.

An alternative approach might be to override the value setting with a custom setter, and put a breakpoint in that, but unfortunately that won't work for IE AFAIK.

UPDATE
It appears that this type of behavior is available at least for unmanaged code written in C++ So I thought maybe a javascript engine written in C++ (Google's V8) might have something similar, but that doesn't appear to have what I want either.

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nadiaa

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3 Years ago

answered 13 Years ago loganl · Accepted Answer

You don't even need an IDE - you can use Object.watch():

Object.Watch Tutorial

If you use any one debugger, I'd strongly recommend Firebug. For all your Javascript, HTML and CSS needs :-):

http://getfirebug.com/javascript

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Update for 2019:

Object.Watch is Ancient History. Uncoincidentally, it's unavailable in most contemporary browsers.

My personal favorite JS debugging tool these days is Chrome Developer Tools.

My personal favorite JS IDE (for Angular, .Net Core, etc) is Microsoft Visual Studio Code (MSVC).

You can do just about any expected debugging operation - including set watches - with the Chrome debugger (just as you could with FF Firebug).

Chrome debugger is well integrated with the MSVC IDE.

Both are free (at least free as in beer); both run well on Windows, Mac and Linux.