redux-intro-walkthrough-comments-manageBand.js

// manageBand is our state manager for Bands.  Basically,
// instead of making changes in component states,
// we're going to be taking care of those state changes here when it
// comes to Bands.

//counter is just for the unique ID for our Delete case.
let counter = 0
export default function manageBand (state = {
  bands: []

  // We can enter manual information into our state like below.
  // bands: [{text: "manual input here"}]
}, action){
  switch(action.type){
    case "ADD_BAND":
      counter++;
      action.band["id"] = counter;
      // returning an object with bands as a key.
      return { bands: state.bands.concat(action.band) };

    case "DELETE_BAND":
       const bands = state.bands.filter( band => band.id !== action.id )
      return { bands }

    default:
    // if we wrapp the below state like { state }, it would have created another object.
    // we would have to say this.props.getState().state.bands
    // without the {}, we just call this.props.getState().bands
      return state
  }

}