nodejs怎么连接数据库

const mysql = require('mysql');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'username',
  password: 'password',
  database: 'database_name'
});

connection.connect((err) => {
  if (err) {
    console.log('Error connecting to database:', err);
    return;
  }
  console.log('Connected to MySQL database');
});

const mongo = require('mongodb');

const MongoClient = mongo.MongoClient;
const url = 'mongodb://localhost:27017';

MongoClient.connect(url, (err, client) => {
  if (err) {
    console.log('Error connecting to database:', err);
    return;
  }
  console.log('Connected to MongoDB database');

  // 使用 client 对象进行数据库操作
});

const pg = require('pg');

const connectionString = 'postgres://username:password@localhost:5432/database_name';

const client = new pg.Client(connectionString);

client.connect((err) => {
  if (err) {
    console.log('Error connecting to database:', err);
    return;
  }
  console.log('Connected to PostgreSQL database');
});