See companion blogpost here: https://medium.com/@valgaze/utility-post-cors-json-p-proxy-servers-and-the-same-origin-policy-7233dec2d26c#.wcmnhsnyo
$ npm run proxy
Then in a browser access: http://localhost:3000/proxy/4
$ npm run jsonp
Then in a browser access: http://localhost:3000/
You need to turn on two servers for this example:
$ npm run cors_server
$ npm run cors_frontend
Then in a browser access: http://localhost:3001/