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Debugging

Projected Time

1.5 to 2 hours

  • 12 minutes for a video walkthrough of slides
  • 45 minutes for Independent Practice #1
  • 30 minutes combined for Independent Practice #2 & Group Practice #1

Prerequisites

Motivation

  • Debugging is the art of finding errors/bugs in programs and determining how to correct them. Things will go wrong during programming, even for experienced software engineers.
  • It is ideally part of the testing process but in reality, it is done at every step of programming. Coders should debug the smallest of their modules before moving on. This decreases the number of errors thrown up during the testing phase and reduces testing time and effort significantly.(reference from tutorialspoint)

Which companies use debugging? Everyone because all companies want their product to be bugs/errors free.

Objectives

Participants will be able to:

  • Understand the various kinds of errors that may arise
  • Use console.log() statements to verify logic and output at different points in the code
  • Use the rubber duck technique to talk through the troublesome code
  • Debug their JS code using Chrome Developer Tools

Specific Things to Learn

  • Types of errors
  • Good debugging strategies
  • Bad debugging strategies

Materials

Lesson

General Tips for Debugging (with VS Code)
  • When VS Code shows you a red squiggly underline then it's trying to help you so I insist you pay attention to the message.
  • If the red squiggly underline is under something that's clearly correct, like color: red; in a CSS file, then first check if it really is correct.
  • Pattern matching — It is a mechanism for checking a value against a pattern. In debugging you use pattern matching (built into VS Code) to match the syntax you write with the correct syntax which helps you to figure out errors in your code. For example, suppose you want to change the color of a text in CSS and you write colour: blue; then VS Code uses its pattern matching mechanism to match it against correct syntax and give you an error "check property spelling" as the correct form is color: blue;.
  • When you make a change on a file, and then visually when you refresh your page you don't see any changes then I suggest you go through the following points:
    • Check whether you saved the file.
      • If you forget then I suggest you add autosave in VS Code.
      • It will help you save the latest changes even if you forget.
      • (How to add autosave in VS Code)
    • Make a temporary, very obvious change on your HTML page.
      • Such as write some text in the top of the body or a prominent heading then save the file and reload the browser.
      • Check whether you can see the text.
      • If you can't see the new text, maybe you have the wrong file open, or the file didn't save, or something else very strange is happening.
    • Make a temporary, very obvious change to your CSS file.
      • such as add color: red; to something extremely obvious like body or h1 then save and reload the browser.
      • Check whether the thing you expected to turn red actually turns red.
      • If it doesn't, maybe the CSS file isn't getting loaded properly or check for syntax errors earlier in your CSS file that may render the rest of your CSS file inoperable.
      • Such as :
        • Are you missing a semicolon?
        • Did you use = instead of : accidentally?
        • Are you missing a quotation mark in a font declaration, so your CSS file thinks there's a really long string somewhere?
        • Are your curly braces correctly matched and closed?

Common Mistakes / Misconceptions

  • "Dang it, I got a bug. Let me ask for help right away." At Techtonica, you should spend at least 20 minutes debugging on your own before asking someone else for help. This is to give yourself the learning opportunity that happens when you struggle, and also to protect other people's time. Once you're in a work setting, ask your manager or teammates how long they expect you to puzzle through something on your own before asking for help.

  • "I don't want anyone to know that I'm struggling with this, even if I have to waste several hours figuring this out on my own." Most managers and colleagues expect that Junior Software Engineers will still need a lot of training and do not expect you to know everything. Learning how to ask strong questions makes you come across as competent and curious, even when you aren't sure about how to do something.

  • "Getting a bug is a personal failure." Nothing is personal with how computers execute your code. Even experienced software engineers get bugs. No one is perfect!

Independent Practice

  1. Techtonica staff will assign pairs. In pairs, work through the Get Started with Debugging JavaScript with Chrome Dev Tools (tutorial).

  2. On their own, each participant writes a program of their choosing using REPL.it and places at least 1 bug in it.

Group Practice

  1. To go with #2 from the Independent Practice: Techtonica staff will assign pairs. Try to debug the program your partner wrote in REPL.it. Swap pairs at least 2 more times so everyone has multiple opportunities to debug someone else's code.

Supplemental Resources

  • https://dzone.com - if StackOverflow & medium had a baby - basically a really well-organized library of technical resources, in-depth subject guides, ref cards/cheat sheets and more. The key is that they bring a teaching + journalistic approach which is fantastic.
  • Debugging Tips and Tricks by Sarah Drasner

Check for Understanding

In a roundtable discussion format, participants share the kinds of bugs they encountered in each other's code, how they were able to identify those bugs, and what they did to fix them.

Answer the following questions:

  • What is debugging?
  • What are bad strategies to implement while you are debugging your code? good?
  • What is a breakpoint and what is it used for?
  • Why should you tell a rubber duck about your programming problem?