#### Principles of redux
1. The entire UI is represented in a single object called *state tree*.
1. The state is *immutable*. Use actions (object) to describe a change and pass it to reducer (function) to create a new state tree.
1. The reducers are pure functions.

#### Reducer signature
```
const exampleReducer = (prevState, actionObj) => {
  return nextState; //don't change/modify prevState to create this
}
```

#### CreateStore method is used to create a redux store. it has 3 main methods
1. getState()
1. dispatch() - this takes action obj as parameter
1. register() - this takes callback to be excecuted after an action is dispatched

#### CombineReducers utility function of redux is used to combine all clild reducers.