Problems with nodeS CORS - node.js

Question

I am trying to display a dicom with NODEJS but the browser throws me this problem
XMLHttpRequest can not load http: // localhost: 8080 / wado?
RequestType = WADO & studyUID = 1.2.840.113704.1.111.5 ... 26513.429 &
contentType = application% 2Fdicom & transferSyntax =
1.2.840.10008.1.2. In 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http: // localhost: 3000' is
therefore not allowed access.
Then install npm the package cors
And here I leave my code part of my code app.js
Var express = require ('express');
Var cors = require ('cors')
App.use (cors ())
App.listen (3000, function () {
  Console.log ('listening on 3000')
})
Also try adding this in app.js
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 ();
});
But the browser still displays the error:
XMLHttpRequest can not load http: // localhost: 8080 / wado?
RequestType = WADO & studyUID = 1.2.840.113704.1.111.5 ... 26513.429 &
contentType = application% 2Fdicom & transferSyntax =
1.2.840.10008.1.2. In 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http: // localhost: 3000' is
therefore not allowed access.
I have doubt because I also use the route index.js which I leave here
var express = require('express');
var router = express.Router();
var cors = require('cors')
/*var express = require('express');
var router = express.Router();*/
var mysql = require('mysql');
router.use(cors({origin: 'http://localhost:3000'}));
/* GET home page. */
router.get('/', function(req, res, next) {
res.render('index', { title: 'Express' });
});
module.exports = router;
I'm sorry for my English

Answer 1

For security purpose browsers don't allow cross origin requests under normal conditions.
Your page is loading from localhost:3000, which defines the origin as it is the first request. Your code is trying to load data from another service running on port- 8080, that is different from origin. So basically you need to enable cors on the service running on port 8080 as it is the external source.