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JavaScript Class Fields — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Class Fields 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

    Declare a field

    easy10 min

    Give the class a count field starting at zero and increase it once.

  2. 2

    Give each instance its own array

    easy10 min

    Push to one basket and report both lengths.

  3. 3

    Use a field in the constructor

    easy10 min

    Build a message from a field and a parameter.

  4. 4

    Override a field

    easy10 min

    Let the constructor replace the field default when a value is given.

  5. 5

    Use an arrow field

    medium10 min

    Make greet an arrow field so it keeps this when detached.

Find the bug(5)

  1. 1

    Fix the field name that does not match

    easy8 min

    The method increases a name that was never declared as a field.

  2. 2

    Fix the shared array

    easy8 min

    A static field is shared, so both baskets see the same items.

  3. 3

    Fix the missing field declaration

    easy8 min

    The class declares no field, so the property does not exist.

  4. 4

    Fix the normal method losing this

    easy8 min

    A detached method needs an arrow field to keep its instance.

  5. 5

    Fix the default wiped by the constructor

    easy8 min

    The constructor assigns even when no value was passed, losing the field's default.

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