Topics

Debugging Errors 


 Slides

Modern Debugging

Traditional debugging:

  • print statements
  • interactive debuggers
  • stack traces
  • rubber ducks

Modern debugging:

  • Google.com
  • StackOverflow.com
  • in-browser dev tools

True Names

"For magic consists in this, the true naming of a thing."   - Ursula LeGuin, A Wizard of Earthsea

to know the true name of an object... or a concept... is to have power over it

SO

you can't google an error until you know the name of the error

Google to Learn

Often, bugs and errors come from programmers not quite understanding the library or language feature they are using.

While reading docs can be tedious, it can help you to understand what problem you're trying to solve...

...even if only to be able to ask for help elsewhere and start by saying, "I've read the docs and I still don't get it."

tech support cheat sheet

tech support cheat sheet

from https://xkcd.com/627/

How to Google

  • First, think of the name of the concept/library/feature/language/tool/error. Remember, names have power.

  • Search for it and half the time you'll find what you're looking for on the first page of results.

  • If the first page is filled with clutter, add a term that distinguishes what you're looking for from all those other results, and search again.

    • Example: god vs god of war vs god of war greece vs god of war game
    • Example: stack vs javascript stack vs javascript stack trace
  • Then once you find the docs, read the whole page.

    • Don't just skim for code snippets!

How to Read

[demo describing how to read MDN, man pages, etc.. Also, always skip W3Schools.]

Google to Debug

If you get an error that you don't understand...

...the first thing to do is not to Google it.

See Anatomy of an Error to learn how to read an error.

Often reading the error reveals enough information to give you an idea for a solution.

Modern Debugging: Step 2

Step 2: google the name of the error

You may find a relevant tutorial, blog post, or StackOverflow answer.

Modern Debugging: Step 3

Step 3: google the name and context of the error

"context" here means either system information (like file paths) or abstract information (like a problem domain, or the name of a package you're using).

  • be aware that some parts of the context will be specific to your personal setup
    • e.g. the first part of full file paths
  • you may need to delete these parts and search again

Modern Debugging: Step 4

Step 4: Stack Overflow

After googling, you will probably find your question answered on StackOverflow.com.

Remember, though: not all answers are correct. You shouldn't just copy and paste code from the first result.

SOOP: StackOverflow Oriented Programming

copy / paste / tweak / repeat

This workflow is far from ideal, but it is acceptable...

... with these caveats:

  • you must have unit tests, to prove that the code
    • (a) does what you want
    • (b) doesn't do anything you don't want
  • you should refactor the code after you get it to work
  • you must at least try to understand it, then mark (with a code comment or commit message) what parts of the code you don't understand
  • you should put a code comment with a link to the StackOverflow answer, so future coders (including you!) can learn more about how it works and why it was needed

Write a Failing Test

When a user reports a bug, the first thing to do is to write a test that exposes the bug, then run it and watch it fail.

This assures that you have actually identified the cause of the bug, and that once you think it's fixed, it's actually fixed.