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JavaScript Array map — exercises and bug fixes

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

    Double every number

    easy10 min

    Use map to double each value and join the result with commas.

  2. 2

    Pull out a property

    easy10 min

    Turn an array of user objects into a comma-separated list of names.

  3. 3

    Uppercase every word

    easy10 min

    Map a list of words to uppercase and join them with spaces.

  4. 4

    Number the list

    easy10 min

    Use the index to build a numbered list separated by pipes.

  5. 5

    Show map keeps the original

    medium10 min

    Map a list to doubles and show the original still joined by commas.

Find the bug(5)

  1. 1

    Fix the missing return

    easy8 min

    A callback with braces must return a value.

  2. 2

    Fix forEach used instead of map

    easy8 min

    forEach gives nothing back, so there is no new array.

  3. 3

    Fix the whole object returned

    easy8 min

    Only the name should come out, not the object itself.

  4. 4

    Fix the result never used

    easy8 min

    map returns a new array; the original is left unchanged.

  5. 5

    Fix the index used as the value

    easy8 min

    The first argument is the value, not the position.

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