how to set access-control-allow-origin in express code example

Example 1: allow cross origin node

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});

Example 2: node express cors headers

var express = require('express')
var cors = require('cors')
var app = express()

app.use(cors())

app.get('/products/:id', function (req, res, next) {
  res.json({msg: 'This is CORS-enabled for all origins!'})
})

app.listen(80, function () {
  console.log('CORS-enabled web server listening on port 80')
})

Example 3: cors package install npm

var express = require('express')var cors = require('cors')var app = express() app.get('/products/:id', cors(), function (req, res, next) {  res.json({msg: 'This is CORS-enabled for a Single Route'})}) app.listen(80, function () {  console.log('CORS-enabled web server listening on port 80')})