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The "Challenge 4" Lesson is part of the full, Reactive Angular 2 with ngrx course featured in this preview video. Here's what you'd learn in this lesson:

In this challenge, you will create immutable methods in the widgets service to create, read, update and delete the widgets collection. - This is only a 10 second video, but I figured I’d still break it up since it follows the format of all the other challenges. If it’s going to be too short or seems weird, we can just combine it with the Challenge 4 solution video.

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