Question

我不断得到

TypeError：country.map不是函数

，我不知道为什么。当我在<Table />中使用注释并使用console.log(tableData)时，它会显示正确的国家/地区数组，但是当我包含<Table />时，我不会得到该数组。

任何帮助将不胜感激！

import React, {useState, useEffect} from 'react';
import {
  MenuItem,
  FormControl,
  Select,
  Card,
  CardContent
} from "@material-ui/core";
import InfoBox from "./InfoBox";
import Map from "./Map";
import './App.css';
import Table from "./Table";

function App() {
  const [countries, setCountries] = useState([]);
  const [country, setCountry] = useState(["worldwide"]);
  const [countryInfo, setCountryInfo] = useState({});
  const [tableData, setTableData] = useState({});

  useEffect(() => {
    fetch('https://disease.sh/v3/covid-19/all')
      .then(response => response.json())
      .then((data) => {
        setCountryInfo(data);
      })
  }, []);

  useEffect(() => {
    const getCountriesData = async () => {
      await fetch("https://disease.sh/v3/covid-19/countries")
        .then((response) => response.json())
        .then((data) => {
          const countries = data.map((country) => (
            {
              name: country.country,
              value: country.countryInfo.iso2
            }
          ));

        setTableData(data);
        setCountries(countries);
      });
    };

    getCountriesData();
  }, []);

  const onCountryChange = async (event) => {
    const countryCode = event.target.value;

    const url = countryCode === 'worldwide' ? 'https://disease.sh/v3/covid-19/all' : `https://disease.sh/v3/covid-19/countries/${countryCode}`;

    await fetch(url)
      .then(response => response.json())
      .then(data => {
        setCountry(countryCode);

        //All data from country
        setCountryInfo(data);
      })
  };

  console.log('COUNTRY INFO >>>', countryInfo);

  return (
    <div className="app">
      <div className="app__left">
        <div className="app__header">
        <h1>COVID-19 STATS</h1>
          <FormControl className="app__dropdown">
            <Select variant="outlined" onChange={onCountryChange} value={country}>
              <MenuItem value="worldwide">Worldwide</MenuItem>
              {
                countries.map((country) => (
                  <MenuItem value={country.value}>{country.name}</MenuItem>
                ))
              }
            </Select>
          </FormControl>
        </div>

        <div className="app__stats">
          <InfoBox title="COVID-19 Cases" cases={countryInfo.todayCases} total={countryInfo.cases} />

          <InfoBox title="Recovered" cases={countryInfo.todayRecovered} total={countryInfo.recovered}/>

          <InfoBox title="Deaths" cases={countryInfo.todayDeaths} total={countryInfo.deaths} />
        </div>

        <Map />
      </div>
      <Card className="app__right">
        <CardContent>
          <h3>Live cases per country</h3>
          {console.log(tableData)}
          <Table countries={tableData} />
          <h3>Worldwide new cases</h3>
        </CardContent>
      </Card>
    </div>
  );
}

export default App;

这是Table.js文件：

import React from 'react'

function Table({ countries }) {
    return <div className="table">
        {countries.map(({ country, cases }) => (
            <tr>
                <td>{country}</td>
                <td>{cases}</td>
            </tr>
        ))}
    </div>
}

export default Table

Answer 1

就像const [tableData, setTableData] = useState({});一样，您正在将tableData设置为对象。另外，API的结果是作为对象的tableData数据，再次设置为对象 setTableData(data);

使用<Table countries={tableData} />组件时，tableData是对象而不是数组。

Answer 2

LoginResponse(user, accessToken)

Answer 3

您还可以添加检查国家/地区是否存在。

countries && countries.map(({ country, cases }) => {}

我不断收到错误消息：“ TypeError：countries.map不是函数”

3 个答案: