如何從函數返回單一類型

Question

我正在嘗試在 Typescript (React) 中構建一個輔助函數。 我定義了一個函數，它根據響應數據返回一個object或object[] 。

現在，當我使用該函數時，返回type是T | T[] T | T[]這需要是基於數據的T或T[] 。

我的幫手功能

import { useQuery } from '@apollo/react-hooks';
import { flatMap } from 'lodash';

export default function QueryHelper<T> (document: any, variables?: {}) {
  const { data: responseData, loading, error } = useQuery(document, { variables });

  const object = (): T => responseData;
  const array = (): T[] => flatMap(responseData);
  let data;

  if (flatMap(responseData).length === 1) {
    data = object();
  } else {
    data = array();
  }
  return { data, loading, error };
}

調用函數

const objects = QueryHelper<Object>(multipleObjectsDocument); 
const object = QueryHelper<Object>(singleObjectDocument, { id });

返回類型

const Object: {
    data: Object| Object[]; // This needs to be 1 type
    loading: boolean;
    error: ApolloError | undefined;
}

主要想法是我可以打電話；

const name = object.data.name';
const listOfName = objects.data.map(obj => obj.name);

現在我收到以下錯誤Property 'map' does not exist on type 'Object | Object[]'. Property 'map' does not exist on type 'Object | Object[]'.

我還嘗試根據 if 語句有條件地返回不同的變量，但這會返回；

const Object: {
    object: Object;
    loading: boolean;
    error: ApolloError | undefined;
} | {
    array: Object[];
    loading: boolean;
    error: ApolloError | undefined;
}

Answer 1

剛修好。

export default function QueryHelper<T> (document: any, variables?: {}): queryResponse<T> {
  const { data: responseData, loading, error } = useQuery(document, { variables });
  let data = responseData ?? [];

  const array = flatMap(data);

  if (!loading && array.length === 1) {
    data = array[0];
  } else {
    data = array;
  }

  return { data, loading, error };
}

電話

const objects = QueryHelper<Object[]>(MultipleObjectsDocument).data; // returns type Object[]
const object = QueryHelper<Object>(ObjectDocument, { id }).data; // returns type Object