Double every number — practice exercise

What you'll be asked to do

1. 1.Double every numberexercise · easy · 10 min

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

   Passes when: #out should show 2,4,6.

2. 2.Pull out a propertyexercise · easy · 10 min · practice plan

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

   Passes when: #out should show Ada,Grace.

3. 3.Uppercase every wordexercise · easy · 10 min · practice plan

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

   Passes when: #out should show RED GREEN.

4. 4.Number the listexercise · easy · 10 min · practice plan

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

   Passes when: #out should show 1:Ada|2:Grace.

5. 5.Show map keeps the originalexercise · medium · 10 min · practice plan

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

   Passes when: #out should show 1,2,3.

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

   A callback with braces must return a value.

   Passes when: #out should show 2,4,6.

7. 7.Fix forEach used instead of mapbug fix · easy · 8 min · practice plan

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

   Passes when: #out should show 10,20.

8. 8.Fix the whole object returnedbug fix · easy · 8 min · practice plan

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

   Passes when: #out should show Ada,Grace.

9. 9.Fix the result never usedbug fix · easy · 8 min · practice plan

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

   Passes when: #out should show red!,green!.

10. 10.Fix the index used as the valuebug fix · easy · 8 min · practice plan

    The first argument is the value, not the position.

    Passes when: #out should show 10,20,30.

Between them these tasks cover map, Transforming data and Callbacks.

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