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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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Setting a data breakpoint is as easy as right-clicking on the property you're interested in watching inside the watch, autos, or locals window and selecting “Break when value changes” in the context menu. All data breakpoints are displayed in the Breakpoints window.
When you reassign a variable to another value, it simply changes the reference to that new value and becomes bound to it.
In Variables view, right-click the variable whose value you want to change and select Change Value. The following table lists where you can find more information about how to update values based on the data type of the variable. 4.
Short answer: no. Immutable is about the behaviour of the value, not about what happens when it's no longer being references: you cannot change an immutable value, you have to instead reassign your variable if you want it to point to a new value.
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.
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