javascript - Break on a change of variable value

Question

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.

Answer 1

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.