text: import { FETCH_WEATHER } from "../actions/index";
  
  export default function(state = [], action) {
      switch (action.type) {
      case FETCH_WEATHER:
          // we want to ADD TO EXISTING CITIES collection, not keep replacing with one last
          // searched city TLDR -> we want to collect cities & their data
          // DO NOT ALTER STATE DIRECTLY!! =>
  
          // state.push([ action.payload.data ])
  
          // concat will return a brand new array, not a mutated old one: 
          // return state.concat([ action.payload.data ]);   SAME AS:
          if(action.payload.data != null) {
              return [ action.payload.data, ...state ];
          }
      }
      return state;
  }