Derive instead of storing — practice exercise

What you'll be asked to do

1. 1.Derive instead of storingexercise · easy · 10 min

   Compute the total from the items rather than keeping a second state.

   Passes when: #total should show 3.

2. 2.Group related fieldsexercise · easy · 10 min · practice plan

   Keep two related values in one state object.

   Passes when: #root should show Ada London.

3. 3.Store an id, not the objectexercise · medium · 10 min · practice plan

   Keep the selected id in state and look the item up.

   Passes when: #value should show second.

4. 4.One status instead of flagsexercise · easy · 10 min · practice plan

   Use a single status string rather than several booleans.

   Passes when: #value should show done.

5. 5.Compute a filtered viewexercise · easy · 10 min · practice plan

   Filter the list for display without storing the filtered copy.

   Passes when: #count should show 2.

6. 6.Fix the duplicated totalbug fix · medium · 8 min

   A stored total goes stale when the list changes.

   Passes when: The total should follow the list.

7. 7.Fix the contradictory flagsbug fix · medium · 8 min · practice plan

   Two booleans allow an impossible state; use one status.

   Passes when: Clicking finish should show done.

8. 8.Fix the copied object in statebug fix · medium · 8 min · practice plan

   A stored copy of the selected item goes stale; store the id.

   Passes when: Clicking should show second.

9. 9.Fix the state initialised from a propbug fix · easy · 8 min · practice plan

   State copied from a prop ignores later prop values.

   Passes when: #value should show Ada.

10. 10.Fix the filtered copy stored in statebug fix · medium · 8 min · practice plan

    The filtered list is stored, so it never updates with the source.

    Passes when: The count should follow the list.

Between them these tasks cover Derived values, Grouping and Single source.

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