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JavaScript classList — exercises and bug fixes

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

    Add a class

    easy10 min

    Add the class active and report the full class list.

  2. 2

    Remove a class

    easy10 min

    Remove the class one and report what is left.

  3. 3

    Toggle a class on

    easy10 min

    Toggle the class open and report whether it is present.

  4. 4

    Check for a class

    easy10 min

    Report whether the element has the class done.

  5. 5

    Add several classes

    medium10 min

    Add three classes at once and report how many the element now has.

Find the bug(5)

  1. 1

    Fix className wiping the other classes

    easy8 min

    Assigning to className replaces every class.

  2. 2

    Fix the dot in the class name

    easy8 min

    classList takes a bare name, without a dot.

  3. 3

    Fix the toggle called twice

    easy8 min

    Toggling twice puts the class back where it started.

  4. 4

    Fix contains used to add

    easy8 min

    contains only checks; it does not change anything.

  5. 5

    Fix the wrong class removed

    easy8 min

    The class that should stay is being taken off.

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