In Node.js, how do I make one server call a function on another server?

Let's say I have 2 web servers. Both of them just installed Node.js and is running a website (using Express). Pretty basic stuff.

How can Server-A tell Server-B to execute a function? (inside node.js)

Preferably...is there a npm module for this that makes it really easy for me?

from In Node.js, how do I make one server call a function on another server?