为什么使用 react-hook 从 API 获取的数据不一致？答案

【问题标题】：Why is data fetched from API using react-hook provided inconsistently?为什么使用 react-hook 从 API 获取的数据不一致？
【发布时间】：2020-09-10 09:03:43
【问题描述】：

我正在尝试使用 React-hook 呈现一些名称字符串。数据是从控制器文件中定义的“/api/getMoreCards”端点获取的，并且工作正常。

问题在于，当我将获取的数据存储到 react-hook 的 useState 对象的“数据”中时，它会不一致地访问数据。让我更具体一点：

import React, {useState, useEffect} from 'react';
import axios from 'axios';
const regeneratorRuntime = require("regenerator-runtime");

const HS = () => {
  const getData = async() => {
    const data = await axios.get('/api/getMoreCards')
    console.log(data)
    setData(data)
}
  const [data, setData] = useState({});
    useEffect(()=>{
      getData()
    },[]);

    return (
      <div>
        <h1>List of Cards</h1>
        **<div>{data.data[0].name}</div>**
      </div>
    );
}
export default HS;

这个文件被导出到 App.js。

在上面的代码中，data.data[0].name 有时会在本地主机上正确呈现，但大多数时候，它会给我以下错误：

“未捕获的类型错误：无法读取未定义的属性'0' 在控制台上的 HS (hsContainer.js:76)"。

在这种情况下，第 7 行的控制台登录根本不会出现在控制台中。

我试过关闭再重新打开VScode，把文件改成'jsx'，把data.data[0].name声明为常量，改变getData和useState代码的顺序，还是不一致。

这是我的 webpack.config.js 和 package.json 文件供参考：

Webpack.config.js

const webpack = require('webpack');
const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');

const config = {
  entry: [
    'react-hot-loader/patch',
    './src/index.js'
  ],
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'bundle.js'
  },
  mode: process.env.NODE_ENV,
  module: {
    rules: [
      {
        test: /\.(js|jsx)$/,
        use: 'babel-loader',
        exclude: /node_modules/
      },
      {
        test: /\.css$/,
        use: [
          'style-loader',
          'css-loader'
        ]
      },
      {
        test: /\.svg$/,
        use: 'file-loader'
      },
      {
        test: /\.png$/,
        use: [
          {
            loader: 'url-loader',
            options: {
              mimetype: 'image/png'
            }
          }
        ]
      }
    ]
  },
  resolve: {
    extensions: [
      '.js',
      '.jsx'
    ],
    alias: {
      'react-dom': '@hot-loader/react-dom'
    }
  },
  devServer: {
        contentBase: './dist',
        proxy: {
            '/api': 'http://localhost:3000',
            '/api/profile': 'http://localhost:3000',
        },
        historyApiFallback: true,
    },
  plugins: [
    new HtmlWebpackPlugin({
        template: `./public/index.html`,
    }),
  ],
};

module.exports = config;

package.json

{
  "name": "Solo-Project",
  "version": "1.0.0",
  "description": "",
  "main": "webpack.config.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "node ./server/server.js",
    "build": "cross-env NODE_ENV=production webpack",
    "devother": "cross-env NODE_ENV=development webpack-dev-server --open --hot & nodemon ./server/server.js",
    "dev": "concurrently \"cross-env NODE_ENV=development webpack-dev-server --open --hot --inline --progress --colors --watch --content-base ./\" \"nodemon ./server/server.js\""
  },
  "repository": {
    "type": "git",
    "url": "git+https://I have replaced this for privacy on stackoverflow.git"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "bugs": {
    "url": "https://I have replaced this for privacy on stackoverflow"
  },
  "homepage": "https://I have replaced this for privacy on stackoverflow",
  "devDependencies": {
    "@babel/core": "^7.11.6",
    "@babel/preset-env": "^7.11.5",
    "@babel/preset-react": "^7.10.4",
    "@hot-loader/react-dom": "^16.13.0",
    "babel-loader": "^8.1.0",
    "css-loader": "^4.3.0",
    "file-loader": "^6.1.0",
    "html-webpack-plugin": "^4.4.1",
    "style-loader": "^1.2.1",
    "url-loader": "^4.1.0",
    "webpack": "^4.44.1",
    "webpack-cli": "^3.3.12",
    "webpack-dev-server": "^3.11.0"
  },
  "dependencies": {
    "axios": "^0.20.0",
    "concurrently": "^5.3.0",
    "cross-env": "^7.0.2",
    "express": "^4.17.1",
    "nodemon": "^2.0.4",
    "react": "^16.13.1",
    "react-dom": "^16.13.1",
    "react-hot-loader": "^4.12.21"
  }
}

【问题讨论】：

标签： get axios react-hooks

【解决方案1】：

当您访问数据时，数据中没有任何内容。要么用一个包含元素的数组来初始化它，要么在渲染之前检查数组是否为空。

const [data, setData] = useState({
    data: [{
        name: "tmp"
    }]
});

// or with optional chaining

return (
    <div> <h1>List of Cards</h1>
       {data?.data?.length && (
            <div>{data.data[0].name}</div>
       )}
    </div>
);

【讨论】：

【解决方案2】：

也可以在渲染前先检查“数据”是否有效

<div>{data && data.data[0].name}</div>

【讨论】：