To make a local server available to the outside world you could use a service like xip.io. Only problem is that xip.io doesn’t play that nice with firewalls and stuff like that.
Recently I used ngrok to solve just that. When started the app creates a tunnel to the ngrok servers, and makes your local server accessible via a (temporary) public URL.
Spend more time programming. One command for an instant, secure URL to your localhost server through any NAT or firewall.
Installation possible via Homebrew Cask:
brew cask install ngrok
You can use instead localtunnel https://github.com/localtunnel/localtunnel for free.