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JavaScript Array filter — exercises and bug fixes

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

    Keep the even numbers

    easy10 min

    Filter a list down to the even numbers and join them with commas.

  2. 2

    Keep the passing scores

    easy10 min

    Filter scores to those of 50 or more and join them with commas.

  3. 3

    Filter objects

    easy10 min

    Keep only the active users and show their names joined by commas.

  4. 4

    Remove empty values

    easy10 min

    Use filter with Boolean to drop the falsy values, then join with commas.

  5. 5

    Filter then map

    medium10 min

    Keep the even numbers, multiply them by 10, and join with commas.

Find the bug(5)

  1. 1

    Fix the missing return in filter

    easy8 min

    Without a return the callback gives undefined, which is falsy.

  2. 2

    Fix the inverted condition

    easy8 min

    The wrong half of the list is being kept.

  3. 3

    Fix map used instead of filter

    easy8 min

    map keeps every element, so the list never shrinks.

  4. 4

    Fix the assignment in the condition

    easy8 min

    A single equals sign assigns instead of comparing.

  5. 5

    Fix the falsy values left in

    easy8 min

    Empty strings and nulls should be removed from the list.

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