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JavaScript try catch — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript try catch 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

    Handle bad JSON

    easy10 min

    Catch the parse failure and report a message.

  2. 2

    Parse valid JSON

    easy10 min

    Parse good JSON and report the name from it.

  3. 3

    Declare the variable outside

    easy10 min

    Keep the value usable after the try block.

  4. 4

    Catch without the parameter

    easy10 min

    Use a catch block that does not name the error.

  5. 5

    Record why it failed

    medium10 min

    Report the error name rather than swallowing it.

Find the bug(5)

  1. 1

    Fix the variable declared inside

    easy8 min

    A variable declared in the try block cannot be read outside it.

  2. 2

    Fix the empty catch

    easy8 min

    Swallowing the error silently hides what happened.

  3. 3

    Fix the try block wrapped too widely

    easy8 min

    Only the parse can fail, so only it belongs inside.

  4. 4

    Fix the catch that reruns the failure

    easy8 min

    Repeating the failing call inside catch throws again.

  5. 5

    Fix the result read before assignment

    easy8 min

    The value is used before the try block has set it.

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