This course has been updated! We now recommend you take the Reactive Angular with NgRx course.

Check out a free preview of the full Reactive Angular 2 course:
The "Challenge 3" Lesson is part of the full, Reactive Angular 2 course featured in this preview video. Here's what you'd learn in this lesson:

In this challenge, students create immutable methods in the widgets service to create, read, update and delete the widgets collection. Then students verify these operations are immutable with Object.freeze.

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