How to pass variable from one child component to another in Angular2?

Question

JavaScript

There are 3 components: parent (P) and 2 children (C1) and (C2) (C1 and C2 are both child components for P and they are not nested)
Template for P looks something like this

<c1-component></c1-component>
<c2-component></c2-component>

c1 has a score variable that needs to be passed to c2 where there is a count_score() method that will add or subtract numbers to it, and then the updated score variable needs to be passed back to c1 from c2 because the count_score() method will be called multiple times. times (accordingly, it will be necessary to add or subtract values ​​already with the updated variable). Tell me, please, how can I solve the problem?
As far as I understand, it is possible through:
1) Shared Service
2) Template and EventEmittler (it seems that this is the best way, I tried to do something, like the other 2 ways, but it doesn’t work out)
3) transfer from c1 to the parent, and from there descend to c2, then from c2 to the parent and from there to c1

Answer 1

Business logic should be in services, and in components only UI, then there will be no such problems