So you want to test your application from you host OS? There are plenty of tips for accessing the host localhost, but finding the information for the other way around has proven difficult, so here it is!
In your VM settings, go to Network and change the "Attached to" property from NAT to Bridged.
Now, all you need to do is find the IP address on the network that your Guest OS is using. So switch to your VM and find out its IP address.
Then open a browser in your host OS and type in the IP address (plus the port if needed). For example,
192.168.1.###:3000 for a typical Linux guest VM).