store

single source of truth
holds application state objects
lets you dispatch actions
and when you create it you have to specify reducers that tells how to state is created
has 3 important methods
- getState()
- dispatch(action);
- subscribe(fn)

action

you cant modify state tree directly, you have to emit an action
action HAS TO HAVE 'type' property

reducers

takes previous state and action, and returns next state
new state has to be new object, but inside that object we can keep old references
they have to be testable
they should specify initial state when called with undefined as state
write test for reducers
reducers can and should call each other
reducers will call everytime an action dispatched (we'll use reselect for memoization)

subscribers

subscribe for the changes of the state (NOT TO THE ACTIONS)

middlewares

use middleware for action subscribing