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JavaScript Method Overriding — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Method Overriding 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

    Override a method

    easy10 min

    Replace the parent's speak with the child's own.

  2. 2

    Use polymorphism

    easy10 min

    Call speak on three different animals and join the answers.

  3. 3

    Extend rather than replace

    easy10 min

    Add to the parent's answer instead of rewriting it.

  4. 4

    Choose the method at runtime

    easy10 min

    One function, two different objects, two different answers.

  5. 5

    Override with the same shape

    medium10 min

    Both formatters take a string and return a string.

Find the bug(5)

  1. 1

    Fix the override with a different name

    easy8 min

    An override must use the same method name.

  2. 2

    Fix the parent's work discarded

    easy8 min

    The child should build on the parent's answer.

  3. 3

    Fix the override on the parent

    easy8 min

    The new behaviour was put on the parent, so every animal barks.

  4. 4

    Fix the missing super in the constructor

    easy8 min

    An overriding constructor still has to call super.

  5. 5

    Fix the override changing the shape

    easy8 min

    The override returns a different kind of value, so it is no longer interchangeable.

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