无法加载资源：部署到Heroku时，服务器的状态为404（未找到）

Question

我有一个带有节点/表达服务器的reactjs应用程序。该应用程序在本地计算机上运行良好。将其很好地部署到Heroku时，它表示构建成功，但是当我访问应用程序网站时，出现“无法获取/”字样，并且在console.log中出现错误无法加载资源：服务器响应状态为404（未找到）。这就是我的目录树的样子，

这是我的根包的样子。我同时运行客户端和服务器，因此即时消息同时使用

{
  "name": "xxxxxxxxxx",
  "version": "0.1.0",
  "private": true,
  "engines": {
    "node": "10.16.3"
  },
  "dependencies": {
    "axios": "^0.19.0",
    "concurrently": "^5.0.2",
    "express": "^4.17.1",
    "google-map-react": "^1.1.5",
    "google-maps-react": "^2.0.2",
    "jquery": "^3.4.1",
    "materialize-css": "^1.0.0-rc.2",
    "node-sass": "^4.13.0",
    "nodemailer": "^6.3.1",
    "nodemon": "^2.0.2",
    "react": "^16.9.0",
    "react-background-slideshow": "^1.0.4",
    "react-dom": "^16.9.0",
    "react-lightgallery": "^0.6.3",
    "react-router-dom": "^5.0.1",
    "react-scripts": "3.1.1",
    "react-scroll-to-component": "^1.0.2",
    "react-tooltip": "^3.11.2",
    "uikit": "^3.1.8"
  },
  "scripts": {
    "client-install": "npm install --prefix client",
    "start": "node server.js",
    "server": "nodemon server.js",
    "client": "npm run start --prefix client",
    "dev": "concurrently \"npm run server\" \"npm run client\"",
    "heroku-postbuild": "NPM_CONFIG_PRODUCTION=false npm install --prefix client && npm run build --prefix client",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  }
}

这是我在客户端文件夹中的包的样子

{
  "name": "client",
  "version": "1.0.0",
  "proxy": "http://localhost:3001",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "dependencies": {
    "axios": "^0.19.0",
    "react-dom": "^16.9.0",
    "react-scripts": "3.1.1"
  },
  "author": "",
  "license": "ISC"
}