Build a counter — practice exercise

What you'll be asked to do

1. 1.Build a counterexercise · easy · 10 min

   Build a counter with a closure and call it three times, joining the results.

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

2. 2.Keep a value privateexercise · easy · 10 min · practice plan

   Store a balance in a closure, deposit 50 onto 100, and show the balance.

   Passes when: #out should show 150.

3. 3.Build a function factoryexercise · easy · 10 min · practice plan

   Make a multiplier that triples, then use it on 14.

   Passes when: #out should show 42.

4. 4.Separate closuresexercise · easy · 10 min · practice plan

   Show that two counters do not share their count, joined by a comma.

   Passes when: #out should show 2,1.

5. 5.Remember whether it ranexercise · medium · 10 min · practice plan

   Use a closure so a setup function only ever returns its first answer.

   Passes when: #out should show first.

6. 6.Fix the counter that resetsbug fix · easy · 8 min

   The count is declared inside the returned function, so it starts again every call.

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

7. 7.Fix the balance that is not keptbug fix · easy · 8 min · practice plan

   The deposit works on a copy, so the balance never grows.

   Passes when: #out should show 150.

8. 8.Fix the factory that returns a numberbug fix · easy · 8 min · practice plan

   The outer function should return a function, not a value.

   Passes when: #out should show 42.

9. 9.Fix the shared countbug fix · easy · 8 min · practice plan

   The count sits outside the factory, so both counters share it.

   Passes when: #out should show 2,1.

10. 10.Fix the loop closurebug fix · easy · 8 min · practice plan

    With var, all three functions share one variable.

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

Between them these tasks cover Closures, Private state and Function factories.

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