为什么我在使用 useState 作为数组时出现错误

Question

import axios from "axios";
import { useEffect, useState } from "react";
import "./styles.css";
export default function App() {
  const [userDataInfo, setUserDataInfo] = useState([]);
  const fetchData = () => {
    axios
      .get("https://random-data-api.com/api/address/random_address")
      .then(function (response) {
        // console.log(response.data);
        return JSON.stringify(response);
      })
      .then(function (data) {
        setUserDataInfo(data);
      });
  };
  useEffect(() => {
    fetchData();
  }, [userDataInfo]);
  return (
    <div className="App">
      {userDataInfo.map((data) => (
        <p>{}</p>
      ))}
    </div>
  );
}
TypeError
userDataInfo.map is not a function
App
/src/App.js:26:20
  23 | 
  24 | return (
  25 |   <div className="App">
> 26 |     {userDataInfo.map((data) => (
     |                  ^
  27 |       <p>{}</p>
  28 |     ))}`enter code here`
  29 |   </div>

Generally, the map() method is used to iterate over an array and call a function on every element of the array and if I am using userDataInfo as an array then why I am getting this error?

Answer 1

 const [userDataInfo, setUserDataInfo] = useState([]);

userDataInfo starts out as an array.

---

 .get("https://random-data-api.com/api/address/random_address")

But then you get that URL which returns a JSON representation of an object (not an array).

---

 return JSON.stringify(response);

And then you convert the object into a string of JSON before storing that string in setUserDataInfo .

---

• Don't convert your data to JSON. JSON is a format useful for sending to external places through APIs (like fetch or localStorage ). It isn't useful for processing data structures internally.
• Do decide what format of data you want to store in userDataInfo . If you are going to store multiple addresses in there, then use an array (and change your handling of the data from the URL to reflect that … eg by adding to an existing array instead of overwriting with a single value). If you are going to use only a single item, then only store a single item (and get rid of the map ).

Answer 2

response object would be in the following format

{
data:"some data"
}

assuming that the api request returns an array then all you need to do is:

axios
      .get("https://random-data-api.com/api/address/random_address")
      .then(function (response) {
        setUserDataInfo(response.data);
      })

perhaps take a look at the axios documentation if need further clarification on the response schema below:

https://axios-http.com/docs/res_schema