Show HN: Time travel debugger for web development

Re:Show HN: Time travel debugger for web development by Lio on Wednesday September 15, 2021 @01:35PM (#28542015)

If you can trigger a debugger from a keyword it's usually pretty easy to trigger it conditionally or on an exception in the code rather than through a GUI.

That works well for ruby and javascript and probably lots of others.

e.g. something like the equivalent of

  def foo
    bar.map do |b|
     b.do_something!
     debugger if b.state == :something_youre_interested_in
    end
  rescue => e
   debugger
  end

I'm really excited by Replay. I think it will be invaluable.

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Re:Show HN: Time travel debugger for web development by lovegoblin on Wednesday September 15, 2021 @05:37PM (#28544699)

Yes, but I think this is what they meant by

> Making watch logic for that sometimes is too complicated or changes the outcome (race conditions especially).

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Re:Show HN: Time travel debugger for web development by HeavyStorm on Saturday September 18, 2021 @12:16AM (#28573662)

Why is that better than using your IDE? Your writing debugging code directly in you production code...

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Re:Show HN: Time travel debugger for web development by tedmielczarek on Thursday September 23, 2021 @12:07PM (#28631135)

I haven't personally used Replay, but from my experience using rr (a native debugger that also provides time-traveling features) being able to replay execution both backwards and forwards in time on a whim is amazing. These tools excel at diagnosing bugs that are hard to reproduce, because you only have to reproduce the bug once under the debugger and then you can endlessly replay that execution until you figure it out. As Jason said above, you can retroactively add print statements in places that would be useful, without having to waste time trying to reproduce the bug again!

roc (the original author of rr) founded a company to build an even more compelling product on top of rr called Pernosco. They have some mind-blowing demos I'd recommend you check out: https://pernos.co/ .

Being able to easily answer questions like "where did the value in this variable come from, and when did it get set?" makes debugging a wildly different experience.

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Re:Show HN: Time travel debugger for web development by sprremix on Sunday September 19, 2021 @08:45AM (#28583889)

How would you debug something inside of a loop (1000s of values) with a line breakpoint in your IDE? Your debugger will trigger the breakpoint every single time it walks through the loop, even when everything is going fine. Now if you conditionally trigger the breakpoint inside the loop using code, it will trigger once and only if it encounters whatever error you want to catch.

Obviously you remove that debug statement from your code after you're finished debugging.

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Re:Show HN: Time travel debugger for web development by ZeikJT on Monday September 20, 2021 @03:04AM (#28591007)

Browsers have conditional breakpoints available in their tools/debuggers so you can write them without changing the code.

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