Multiple domain names globalisation strategy in NodeJS

I have 4 domain names .com .com.au .co.nz and .co.uk I am usign NodeJS and hosted on Heroku.

I would like to know (because this is the first time I am doing this) how to say if the user comes from Australia then go to .com.au and display results only for that country. By default would be .com domain

Question:

1. Should I create different apps, databases for each country?
2. Can I use same app and same database for everything?
3. Which is the best approach to do that?
4. Is there a NPM module that I can install that helps me with this sort of configuration?

I see a lot of classifieds websites like olx.com and also in Airbnb, the are using local strategy.

Thank you, I will appreciate a lot your help.

via Matt