reducer.js

function person(state, action) {
  state = state || {};

  switch(action.type){
    case 'ADD_INFO':
      return Object.assign({}, state, action.payload);
    default:
      return state;
  }
}

function hoursWorked(state, action) {
  state = state || 0;

  switch(action.type){
    case 'ADD_HOUR':
      return state + 1;
    case 'SUBTRACT_HOUR':
      return state - 1;
    default:
      return state;
  }
}

var myReducers = {
  person: person,
  hoursWorked: hoursWorked
};

function combineReducers(reducers) {
  return function(state, action) {
    state = state || {};

    return Object.keys(reducers).reduce(function(nextState, key) {
      nextState[key] = reducers[key](state[key], action);
      return nextState;
    }, {});
  };
}

var rootReducer = combineReducers(myReducers);
var firstState = rootReducer(undefined, {type: 'ADD_INFO', payload: {name: 'Brian'}});
var secondState = rootReducer({hoursWorked: 10, person: {name: 'Joe'}}, {type: 'ADD_HOUR'});

console.log('***FIRST STATE***:', firstState);
console.log('***SECOND STATE***:', secondState);