• Reducer reduce a set of actions (over time) into a single state.

• Important Rule of Reducer:
  • Never return undefined from a reducer.
  • Reducers must be pure functions.
• Actions are very free-formed things, as long as it’s an object with a type.

  convention: types are plain strings, and often uppercased.

• Actions don’t really do anything on their own. In order to make an action DO something, you need to dispatch it.

• Call dispatch with an action, and Redux will call reducer with that action (and then replace the state with whatever the reducer returns).