与 Typescript 反应：“never[]”类型的参数不可分配给“StateProperties |”类型的参数 (() => 状态属性)'

Question

I am practicing typescript. For the backend, I used node express typescript and for the frontend, I used react typeScript. I fetched the data from the backend and try to render it on my browser. I am getting an error: property 'name' does not exist on type 'never'. TS2339 property 'name' does not exist on type 'never'. TS2339 . I think this error is coming from typescript. This is the error visualization

This is my backend setup

import express = require("express");
import cors = require("cors");
const app = express();
app.use(cors());
const port = 8080;
app.get("/", (req, res) =>
  res.send([
    {
      name: "John",
      age: 36
    },
    {
      name: "alex",
      age: 27
    }
  ])
);

app.listen(port, () => console.log(`server running port ${port}`));

This is is my React component

    import React, { useEffect, useState } from "react";

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

//StateProperties | (() => StateProperties)
function App() {
  const [state, setState] = useState<StateProperties>([]);

  useEffect(() => {
    getData();
  }, []);

  const getData = async () => {
    const response = await fetch("http://localhost:8080/");
    const data = await response.json();
    console.log(data);
    setState(data);
  };

  return (
    <div className="App">
      {state.length}

      {state.map((list, index) => {
        return <li key={index}>{list.name}</li>;
      })}
    </div>
  );
}

export default App;

Answer 1

You need to provide the interfaces/type aliases so that TypeScript will know the typings of state .

After creating the interface for state , you will need to provide the interface as the generics for useState .

To solve the 2nd issue, you will need to provide the key props to each item of the <li> element

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

function App() {
  const [state, setState] = useState<StateProperties[]>([]);

  // do the rest

return (
  <div className="App">
    {state.map(({ name, age }) => {
      return <li key={`${name}-${age}`}>{name}</li>; //FROM HERE ERROR IS COMING
    })}
  </div>
  );

}