README.md

Reactive Operators exercise

Exercise 1: Pop Quiz App

This is actually the same exercise we have done in Module 10. In the original exercise we used a lot of behavior subjects for information that was derived from other subjects. And we used the service, to do the synchronization (whenever we pushed a value to one of the atomic subjects, we also updated the derived ones). This is bad architecture.

In this exercise you will fix the application by replacing the derived behavior subjects with observables that will be created using operators. So they will be automatically updated.

Targets

• Using Observables
• Using RxJS operators

Steps

• The _currentQuestion$ and _previousAnswer subjects are the atomic ones, and they should remain. But we do want to ranme them internally: _questions$ and _answers$.
• Now the implementation of answerCurrentQuestion and createNewQuestion are simple:
  • answerCurrentQuestion only pushes a new answer to the _answers$ subject and then call createNewQuestion
  • createNewQuestion only pushes a new question to the _questions$ subject
• All the rest of the observables should be derived using operators:
  1. Implement the currentQuestion$ observable. (Trivial)
  2. Implement the previousQuestion$ observable. (Hint - use the bufferCount operator)
  3. Implement the previousAnswer$ observable. This is actually quite simple, since this is the latest answer.
  4. Implement the score$, rank$, isPreviousQuestionCorrect$ observables. To do that,
     • Start by creating a questionAnswer$ observable of type: Observable<[Question, Answer]>. This observable will push the next pair of question + answer. (Hint, use zip to pair together questions and answers)
     • Now create a history$ observable of type Observable<[Question, Answer][]>. Each event will hold the entire list of questions that were answered as question+answer pair. (Hint, use scan to derive it from questionAnswer$)
     • Now you can use map to create score$ which is the accumulated score.
     • In the same way you can derive rank$ and isPreviousQuestionCorrect$ from the history$ observable using map. Each time implement the mapping function seperatly as a pure function