bookSubjectModifierReducer.js

const bookSubjectManagerInitialState = () => ({
    singleBookModify: null,
    selectedBooksModify: false,
    addingSubjects: {},
    removingSubjects: {}
});

function bookSubjectManagerReducer(state = bookSubjectManagerInitialState(), action = {}){
    switch (action.type){
        case ENABLE_SUBJECT_MODIFICATION_FOR_SINGLE_BOOK:
            return Object.assign({}, state, { singleBookModify: action._id });
        case ENABLE_SUBJECT_MODIFICATION_FOR_TOGGLED_BOOKS:
            return Object.assign({}, state, { selectedBooksModify: true });
        case CANCEL_SUBJECT_MODIFICATION:
            return Object.assign({}, state, { singleBookModify: null, selectedBooksModify: false });
        case TOGGLE_SUBJECT_ADD_FOR_SUBJECT_MODIFICATION:
            return Object.assign({}, state, { addingSubjects: { ...state.addingSubjects, [action._id]: !state.addingSubjects[action._id] } });
        case TOGGLE_SUBJECT_REMOVE_FOR_SUBJECT_MODIFICATION:
            return Object.assign({}, state, { removingSubjects: { ...state.removingSubjects, [action._id]: !state.removingSubjects[action._id] } });
    }
    return state;
}