If you got this issue in Ionic:

Origin http://localhost:8100 is not allowed by Access-Control-Allow-Origin.

It is because you are running node.js and ionic serve project on localhost and trying to access two different ports which causes a cross origin access error.

To fix this simply edit your ionic.project file to map out the linking like this:

{
  "name": "proxy-example",
  "app_id": "",
  "proxies": [
    {
      "path": "/signUp",
      "proxyUrl": "http://localhost:3000/signUp"
    },
     {
      "path": "/checkSession",
      "proxyUrl": "http://localhost:3000/checkSession"
    },
     {
      "path": "/login",
      "proxyUrl": "http://localhost:3000/login"
    },
     {
      "path": "/logout",
      "proxyUrl": "http://localhost:3000/logout"
    }
  ]
}

Now in your Ionic project you can call localhost:8100/login for example and it will call localhost:3000/login which the port node.js server is running on.

Web App Only Solution

If you are only making a web app for the browser and not running as a native app, then you can just move the angular portion of the code into the server part.

Copy the /www folder from your frontend into the server /public folder. You can then access your UI from http://localhost:3000.

I hope this makes sense to you.