How to create interface for array of objects in usestate in react js

Question

I made a request with AXIOS to the server and then the server returned the value as follows:

I want to save it in state, here I use react hooks, when I want to set state with data as shown I get error:

Argument of type '() => IterableIterator<IMahasiswa>' is not assignable to parameter of type 'SetStateAction<undefined>'.
  Type 'IterableIterator<IMahasiswa>' is not assignable to type 'undefined'.ts(2345)

and this is my code:

and my interface:

how do I set the interface for setMahasiswa I have tried <IMahasiswa[]> but it gives the same error, except that in the res.values section it is replaced with res it is successfully returned, but it will throw another error when I using map for looping

Did you actually get the exact same error when using <IMahasiswa[]>? Can you include that error message? — Henry
– Henry, Commented Jun 27, 2021 at 2:08

choz · Accepted Answer · 2021-06-27 02:17:21Z

My assumption is that your axios.get(url[, config]) returns an any type by default. So, your data there also has any type unless you cast it to IMahasiswa[].

However, my suggested solution is to define the type at axios.get, here's the outline from their typedef.

export interface AxiosInstance {
  //...
  get<T = any, R = AxiosResponse<T>>(url: string, config?: AxiosRequestConfig): Promise<R>;
  //...
}

Therefore, you can do something like this;

await axiosClient.get<IMahasiswa[]>("asd/asd", {});

Here's the full code example;

interface IMahasiswa {
  name: string;
  age: number;
}

const useTest = () => ({
  async fetch(): Promise<IMahasiswa[]> {
    const { data } = await axiosClient.get<IMahasiswa[]>("asd/asd", {});
    return data; // data here has the type of IMahasiswa[]
  },
});

const axiosClient = axios.create({
  baseURL: "http://localhost:1231",
});

const TestComp = () => {
  const [mahasiswa, setMahasiswa] = React.useState<IMahasiswa[]>([]);
  const testFn = useTest();

  useEffect(() => {
    testFn.fetch().then((res) => {
      setMahasiswa(res);
    });
  }, []);

  return <div>asd</div>;
};

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