express cors error

1var express = require('express')
2var cors = require('cors')
3var app = express()
4
5app.use(cors())
6
7app.get('/products/:id', function (req, res, next) {
8  res.json({msg: 'This is CORS-enabled for all origins!'})
9})
10
11app.listen(80, function () {
12  console.log('CORS-enabled web server listening on port 80')
13})
14

1var express = require('express')
2var cors = require('cors')  //use this
3var app = express()
4
5app.use(cors()) //and this
6
7app.get('/user/:id', function (req, res, next) {
8  res.json({user: 'CORS enabled'})
9})
10
11app.listen(5000, function () {
12  console.log('CORS-enabled web server listening on port 5000')
13})

1// CORS (Cross-Origin Resource Sharing) headers to support Cross-site HTTP requests
2
3app.all('*', function(req, res, next) {
4       res.header("Access-Control-Allow-Origin", "*");
5       res.header("Access-Control-Allow-Headers", "X-Requested-With");
6       res.header('Access-Control-Allow-Headers', 'Content-Type');
7       next();
8});
9

1//install
2npm install cors
3//use
4var express = require('express')
5var cors = require('cors')
6var app = express()
7
8app.use(cors())
9
10app.get('/products/:id', function (req, res, next) {
11  res.json({msg: 'This is CORS-enabled for all origins!'})
12})
13
14app.listen(80, function () {
15  console.log('CORS-enabled web server listening on port 80')
16})
17

1var allowedOrigins = ['http://localhost:3000',
2                      'http://yourapp.com'];
3app.use(cors({  
4  origin: function(origin, callback){
5    // allow requests with no origin     
6    // (like mobile apps or curl requests)    
7    if(!origin) 
8      return callback(null, true);    
9    if(allowedOrigins.indexOf(origin) === -1){
10      var msg = 'The CORS policy for this site does not ' +                
11          'allow access from the specified Origin.';      
12      return callback(new Error(msg), false);    
13    }    
14    return callback(null, true);  
15  }
16}));

1$ npm install cors
2