Call next manually — practice exercise

What you'll be asked to do

1. 1.Call next manuallyexercise · easy · 10 min

   Get an array's iterator and read its first value.

   Passes when: #out should show 1.

2. 2.Check the done flagexercise · easy · 10 min · practice plan

   Drain a one-element array and check the second call is done.

   Passes when: #out should show true.

3. 3.Write a custom iteratorexercise · easy · 10 min · practice plan

   Build an iterator object that counts to three.

   Passes when: #out should show 1.

4. 4.Drain an iterator by handexercise · easy · 10 min · practice plan

   Collect every value from a custom iterator into an array.

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

5. 5.Check for the iterator methodexercise · medium · 10 min · practice plan

   Report whether a plain object has Symbol.iterator.

   Passes when: #out should show no.

6. 6.Fix the value read as the whole resultbug fix · easy · 8 min

   next() returns an object; the value is one property of it.

   Passes when: #out should show 1.

7. 7.Fix the loop that never stopsbug fix · easy · 8 min · practice plan

   Without checking done, the loop keeps calling next past the end.

   Passes when: #out should show 3 values.

8. 8.Fix the custom iterator returning a value with done truebug fix · easy · 8 min · practice plan

   Once finished, value should be undefined, not a leftover number.

   Passes when: #out should show reached the end.

9. 9.Fix the plain object assumed to be iterablebug fix · easy · 8 min · practice plan

   A plain object has no Symbol.iterator method, so spreading it throws.

   Passes when: #out should show not iterable.

10. 10.Fix done checked with the wrong valuebug fix · easy · 8 min · practice plan

    done is a boolean, not the string "true".

    Passes when: #out should show is finished.

Between them these tasks cover Iterator protocol, next() and done.

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