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JavaScript Higher Order Functions — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Higher Order Functions 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

    Transform with map

    easy10 min

    Add 20 percent to each price and join the results with commas.

  2. 2

    Keep some with filter

    easy10 min

    Keep only numbers above 4 and join them with commas.

  3. 3

    Total with reduce

    easy10 min

    Add 1, 2, 3 and 4 together using reduce.

  4. 4

    Return a function

    easy10 min

    Write a function that builds a multiplier, then triple 15.

  5. 5

    Chain them together

    medium10 min

    Keep the even numbers from 1 to 6, multiply each by 10, and add them up.

Find the bug(5)

  1. 1

    Fix forEach used instead of map

    easy8 min

    forEach returns nothing, so there is no new array.

  2. 2

    Fix the filter that returns nothing

    easy8 min

    The callback has braces but no return, so nothing is kept.

  3. 3

    Fix the missing starting value

    easy8 min

    Without a starting value the first item is used as the total.

  4. 4

    Fix the function called instead of returned

    easy8 min

    The outer function returns a number, not a function.

  5. 5

    Fix the wrong chain order

    easy8 min

    Multiplying before filtering changes which numbers are kept.

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