由于某种原因，我的代码只显示一次，当我刷新页面时，我开始出现错误

Question

import React from "react";
import { useParams } from "react-router-dom";
import { useState, useEffect } from "react";

const SingleUser = () => {
  const [user, setUser] = useState([]);
  const { username } = useParams();

  useEffect(() => {
    const getSingleUser = async () => {
      try {
        const res = await fetch(
          `https://api.chess.com/pub/player/${username}/stats`
        );
        const data = await res.json();
        const heroesArray = Object.values(data);
        setUser(heroesArray);
        console.log(heroesArray[0].last);
      } catch (error) {
        console.error(error);
      }
    };

    getSingleUser();
  }, []);

  return (
    <section>
      <div>
        <h1>Rapid Chess</h1>
        <p>Current Rating: {user[0].last.rating}</p>
        <p>Best Rating: {user[0].best.rating} </p>
        <div>
          <p>Wins: {user[0].record.win} </p>
          <p>Losses: {user[0].record.loss} </p>
          <p>Draws: {user[0].record.draw} </p>
        </div>
      </div>
     
    
    </section>
  );
};

export default SingleUser;

由于某种原因，我的代码只显示一次，当我刷新页面时，我开始出现错误。我认为这与 useEffect 有关，但我不知道

类型错误：无法读取未定义的属性（读取“最后”）。我收到这些错误。

Answer 1

当您处理来自 api 的数据时，您应该使用 可选链，因为数据可能会也可能不会：

import React from "react";
import { useParams } from "react-router-dom";
import { useState, useEffect } from "react";

const SingleUser = () => {
  const [user, setUser] = useState([]);
  const { username } = useParams();

  useEffect(() => {
    const getSingleUser = async () => {
      try {
        const res = await fetch(
          `https://api.chess.com/pub/player/${username}/stats`
        );
        const data = await res.json();
        const heroesArray = Object.values(data);
        setUser(heroesArray);
        console.log(heroesArray?.[0]?.last);
      } catch (error) {
        console.error(error);
      }
    };

    getSingleUser();
  }, []);

  return (
    

      

        
Rapid Chess
        
Current Rating: {user?.[0]?.last?.rating}
        
Best Rating: {user?.[0]?.best?.rating} 
        

          
Wins: {user?.[0]?.record?.win} 
          
Losses: {user?.[0]?.record?.loss} 
          
Draws: {user?.[0]?.record?.draw} 
        
      
     
    
    
  );
};

export default SingleUser;