if (action.type == types.FILTER_TITLE_CHANGED) {
let newState = { ...state };
newState.filterTitleStr = action.filterTitleStr;
return newState;
} else if (action.type == types.FILTER_AUTHOR_CHANGED) {
let newState = { ...state };
newState.filterAuthorStr = action.filterAuthorStr;
return newState;
} else if (action.type == types.FILTER_CATEGORY_CHANGED) {
let newState = { ...state };
newState.filterCategoryStr = action.filterCategoryStr;
return newState;
}