快递没有定义..??即使在安装后

Question

my code under package.json

{
"name": "mernstack",
"version": "1.0.0",
"description": "social network for developers",
"main": "server.js",
"scripts": {
"start": "node server.js",
"server": "nodemon server.js"
},
"author": "sonali",
"license": "MIT",
"dependencies": {
"bcrypt": "^2.0.1",
"bcryptjs": "^2.4.3",
"express": "^4.16.3",
"gravatar": "^1.6.0",
"mongoose": "^5.1.6",
"passport": "^0.4.0",
"passport-jwt": "^4.0.0",
"validator": "^10.4.0"
},
"devDependencies": {
"eslint": "^4.19.1",
"nodemon": "^1.17.5"
}
}

即使它之前运行良好，我也会收到此错误...？？ 收到此错误后，我重新安装了Express，当时它显示字节错误 收到该错误后，我卸载了npm并重新安装了它，之后我收到此错误，请帮助我

Answer 1

如果我们可以看到您的代码会更容易，但是您是否正确初始化了表达式？

const express = require('express');
const app = express();

Answer 2

您必须在应用程序中实例化 express

。

const express = require('express');
const app = express();

或者，如果您使用的是新导入

import express from 'express';