gengitkan/client/src/store/reducers/issues.js

import { FETCH_ISSUES_SUCCESS } from "../actions/issues";

const defaultState = {
  byProject: {}
};

export function issuesReducer(state = defaultState, action) {
  switch(action.type) {
    case FETCH_ISSUES_SUCCESS:
      return handleFetchIssuesSuccess(state, action);
    default:
      return state;
  }
  
}

function handleFetchIssuesSuccess(state, action) {
  return {
    ...state,
    byProject: {
      ...state.byProject,
      [action.project]: [
        ...action.issues,
      ]
    }
  }
}