# install packages 
npm i express sequalize cors pg

Configurar servidor el servidor

const express = require("express");
const cors = require("cors");

const app = express();

var corsOptions = {
  origin: "<http://localhost:8081>"
};

app.use(cors(corsOptions));

// parse requests of content-type - application/json
app.use(express.json());

// parse requests of content-type - application/x-www-form-urlencoded
app.use(express.urlencoded({ extended: true }));

// simple route
app.get("/", (req, res) => {
  res.json({ message: "Welcome to application." });
});

// set port, listen for requests
const PORT = process.env.PORT || 8080;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}.`);
});

# para acceder a las variables de .env a traves de process.env en js
npm install --save dotenv
# used for helping us to set the NODE_ENV in any command line, without worrying about the operating system
npm install --save-dev cross-env
# a middleware used with express to get request’s body as an Object.
npm install --save-dev body-parser