I am attempting to edit a file. Emacs is preventing me from making the edit, and throwing: Args out of range: #<buffer user.action.js>, 4965, 17721. It is completely not obvious to me where this exception is coming from. How can I debug errors such as this one?

  • @Drew: the similarity between the two seems rather tenuous.
    – Stefan
    Sep 26, 2018 at 15:21
  • @stefan: Indeed; sorry. The question is essentially how to see what happened & why, when an error is raised - catch the error and show a call stack. A general answer is, as you suggested, to show a backtrace via debug-on-error. Seems like the question has been asked, but I don't find a good duplicate.
    – Drew
    Sep 26, 2018 at 16:00

1 Answer 1


Enable debugging via M-x toggle-debug-on-error or in the menu Options => Enter Debugger on Error.

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