Declare a private field — practice exercise

What you'll be asked to do

1. 1.Declare a private fieldexercise · easy · 10 min

   Keep the balance private and expose it through a method.

   Passes when: #out should show 100.

2. 2.Hide it from Object.keysexercise · easy · 10 min · practice plan

   Report the keys of an object with one private and one public field.

   Passes when: #out should show name.

3. 3.Control how it changesexercise · easy · 10 min · practice plan

   Refuse a negative deposit and report the balance.

   Passes when: #out should show 100.

4. 4.Write a private methodexercise · easy · 10 min · practice plan

   Keep the tax calculation private and use it from total.

   Passes when: #out should show 120.

5. 5.Expose it through a getterexercise · medium · 10 min · practice plan

   Give the class a balance getter that reads the private field.

   Passes when: #out should show 250.

6. 6.Fix the underscore conventionbug fix · easy · 8 min

   An underscore does not actually prevent anything.

   Passes when: #out should show 100.

7. 7.Fix the private field exposedbug fix · easy · 8 min · practice plan

   The field is public, so it shows up in Object.keys.

   Passes when: #out should show only name.

8. 8.Fix the missing validationbug fix · easy · 8 min · practice plan

   A negative deposit is being accepted.

   Passes when: #out should show 100.

9. 9.Fix the helper left publicbug fix · easy · 8 min · practice plan

   The tax helper should not be callable from outside.

   Passes when: #out should show private.

10. 10.Fix the private field read from outsidebug fix · easy · 8 min · practice plan

    A private field can only be reached from inside the class body.

    Passes when: #out should show 250.

Between them these tasks cover Private fields, Encapsulation and Private methods.

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