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JavaScript Error Handling Patterns — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Error Handling Patterns lesson. Every one is checked automatically in the browser — write the code, run it, and the tests tell you what still fails.

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Exercises(5)

  1. 1

    Return a fallback

    easy10 min

    Parse the text and return null when it fails.

  2. 2

    Fail fast on bad input

    easy10 min

    Check the types at the top and throw immediately.

  3. 3

    Use a guard clause

    easy10 min

    Return a default rather than throwing for missing input.

  4. 4

    Add context when rethrowing

    easy10 min

    Replace the parse error with a clearer message.

  5. 5

    Handle at the boundary

    medium10 min

    Let the loop fail and catch once at the top.

Find the bug(5)

  1. 1

    Fix the missing input check

    easy8 min

    With no check the text is coerced and a wrong answer is returned.

  2. 2

    Fix the error caught and ignored

    easy8 min

    Catching without acting hides a genuine bug.

  3. 3

    Fix the rethrow with no new information

    easy8 min

    Rethrowing the same message adds nothing.

  4. 4

    Fix the throw where a default would do

    easy8 min

    A missing name is expected, so return a greeting instead.

  5. 5

    Fix the handler inside the loop

    easy8 min

    One handler at the boundary is enough.

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