Add up a list — practice exercise

What you'll be asked to do

1. 1.Add up a listexercise · easy · 10 min

   Use reduce to total a list of numbers.

   Passes when: #out should show 60.

2. 2.Handle an empty arrayexercise · easy · 10 min · practice plan

   Reduce an empty array with a starting value of zero.

   Passes when: #out should show 0.

3. 3.Find the largestexercise · easy · 10 min · practice plan

   Use reduce to find the biggest number in a list.

   Passes when: #out should show 44.

4. 4.Build a stringexercise · easy · 10 min · practice plan

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

   Passes when: #out should show code.

5. 5.Count occurrencesexercise · medium · 10 min · practice plan

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

   Passes when: #out should show 2.

6. 6.Fix the missing accumulator returnbug fix · easy · 8 min

   The callback must return the accumulator for the next turn.

   Passes when: #out should show 60.

7. 7.Fix the wrong starting valuebug fix · easy · 8 min · practice plan

   Starting at one adds an extra to the total.

   Passes when: #out should show 60.

8. 8.Fix the arguments swappedbug fix · easy · 8 min · practice plan

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

   Passes when: #out should show code.

9. 9.Fix the string starting valuebug fix · easy · 8 min · practice plan

   Starting with a string turns the addition into text joining.

   Passes when: #out should show 60.

10. 10.Fix the largest comparisonbug fix · easy · 8 min · practice plan

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

    Passes when: #out should show 44.

Between them these tasks cover reduce, Accumulators and Starting values.

Looking for a different chapter? See every practice set, or switch to the interview theory questions.