Node.js 当我尝试使用env变量连接React和nodejs时，看起来像React不向nodejs发送请求

我已经完成了你的Node JS课程，然后开始了你的React JS课程。现在我也几乎完成了你的反应课程

我将Reactjs连接到节点JS，直到添加了config.env变量它才正常工作，当我在nodejs中添加config/dev.env并添加命令“dev”：“env cmd./config/dev.env nodemon server/server.JS”时，它并没有向节点JS发送请求。当我删除env cmd./config/dev.env时，我的应用程序开始运行“dev”：“nodemon server/server.js”

请帮我解决这个问题

package.json文件

    {
  "name": "moneymanage",
  "version": "1.0.0",
  "main": "index.js",
  "author": "Poorna",
  "license": "MIT",
  "scripts": {
    "serve": "live-server public/",
    "build:dev": "webpack",
    "build:prod": "webpack -p --env production",
    "dev-server": "webpack-dev-server",
    "dev": "env-cmd ./config/dev.env nodemon server/server.js",
    "test": "jest --config=jest.config.json",
    "start": "node server/server.js",
    "heroku-postbuild": "yarn run build:prod"
  },
  "dependencies": {
    "@babel/core": "^7.11.6",
    "@babel/preset-env": "^7.11.5",
    "@babel/preset-react": "^7.10.4",
    "@material-ui/core": "^4.11.0",
    "@material-ui/icons": "^4.9.1",
    "axios": "^0.21.0",
    "babel-cli": "^6.26.0",
    "babel-loader": "^8.1.0",
    "babel-plugin-transform-class-properties": "^6.24.1",
    "babel-plugin-transform-object-rest-spread": "^6.26.0",
    "babel-preset-env": "^1.7.0",
    "babel-preset-react": "^6.24.1",
    "bootstrap": "^4.5.3",
    "cors": "^2.8.5",
    "css-loader": "^4.3.0",
    "express": "4.16.4",
    "extract-text-webpack-plugin": "3.0.0",
    "firebase": "^7.24.0",
    "install": "^0.13.0",
    "mini-css-extract-plugin": "^1.0.0",
    "moment": "^2.29.1",
    "mongodb": "3.1.10",
    "mongoose": "5.3.16",
    "node-sass": "^4.14.1",
    "normalize.css": "^8.0.1",
    "npm": "^6.14.8",
    "numeral": "^2.0.6",
    "react": "^16.13.1",
    "react-addons-shallow-compare": "^15.6.2",
    "react-bootstrap": "^1.4.0",
    "react-dates": "12.3.0",
    "react-dom": "^16.13.1",
    "react-modal": "^3.11.2",
    "react-redux": "^7.2.1",
    "react-router-dom": "^5.2.0",
    "redux": "^4.0.5",
    "redux-thunk": "^2.3.0",
    "sass-loader": "^10.0.2",
    "style-loader": "^1.3.0",
    "uuid": "^8.3.1",
    "validator": "^13.1.17",
    "webpack": "^4.44.2",
    "webpack-cli": "^3.3.12",
    "webpack-dev-server": "^3.11.0"
  },
  "devDependencies": {
    "cross-env": "^7.0.2",
    "dotenv": "^8.2.0",
    "env-cmd": "8.0.2",
    "jest": "^26.5.3",
    "live-server": "^1.2.1",
    "nodemon": "1.18.9"
  }
}

项目文件夹结构

尝试向NodeJS发送数据时的React代码

import axios from 'axios';

   axios
      .post('http://localhost:3000/create', expensesData)
      .then((response) => {
        console.log(response.data);
        this.setState({events: response.data})
      })
      .catch(err => {
        console.error('error: ', err);
      });

---

express服务器中的端口是什么？您是否与服务器并行运行react应用程序？3000/3001端口号。是，通过node js运行react应用程序。您需要在express服务器和react应用程序之间创建一个代理。这里有一个例子：最后它成功了，我在代理中写了错误的url。