On this session I am going to talk about pure function called – reducer (or ‘stepper’). Usually people use this function in context of most base transformation function Array.prototype.reduce(reducer, state) but reducers can be applied not only for this certain case. We will see how we can scale out our back-end architecture with reducers in context of CQRS and Event Sourcing. Also we will see how to apply this technique for front-end architecture and what benefits we can gain.

1. Reducers in Action
Anton Moldovan
EY
@antyadev

2. About me:
@AntyaDev
like types*

7. Is an architectural pattern proposed
by Greg Young that segregates reads
and writes of system into two separate
subsystems.

9. Capture intent
Easy to Scale

15. append only

24. Reducer<I,E> :: (I, E) -> I
A pure function that takes an initial value and an element,
and returns a new value for the initial item

25. const counter = (state, action) => {
switch (action.type) {
case 'INCREMENT': return state + 1;
case 'DECREMENT': return state – 1;
default: return state;
}
}
(state, action) => state

26. Mutate its arguments
Perform side effects like API calls
Calling non-pure functions like Date.now() or Math.random()

27. TheProblem

28. Greg Young • Event Sourcing
https://www.youtube.com/watch?v=8JKjvY4etTY
GregYoung 8 CQRS Class
https://www.youtube.com/watch?v=whCk1Q87_ZI
Timelines at Scale
http://www.infoq.com/presentations/Twitter-Timeline-Scalability
Redux
http://redux.js.org/index.html

29. @antyadev