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JavaScript Array reduce — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Array reduce 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 up a list

    easy10 min

    Use reduce to total a list of numbers.

  2. 2

    Handle an empty array

    easy10 min

    Reduce an empty array with a starting value of zero.

  3. 3

    Find the largest

    easy10 min

    Use reduce to find the biggest number in a list.

  4. 4

    Build a string

    easy10 min

    Use reduce to glue an array of letters into one word.

  5. 5

    Count occurrences

    medium10 min

    Use reduce with an object to count how many times yes appears.

Find the bug(5)

  1. 1

    Fix the missing accumulator return

    easy8 min

    The callback must return the accumulator for the next turn.

  2. 2

    Fix the wrong starting value

    easy8 min

    Starting at one adds an extra to the total.

  3. 3

    Fix the arguments swapped

    easy8 min

    The value is being put before the accumulator, so the word comes out backwards.

  4. 4

    Fix the string starting value

    easy8 min

    Starting with a string turns the addition into text joining.

  5. 5

    Fix the largest comparison

    easy8 min

    The comparison keeps the smaller value instead of the bigger one.

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