NodeJS - Requiring module returns empty array

EDIT

exporting with ES6 is a little nicer

export const hello = function(){
  console.log('hello');
};

importing will look like

import {hello} from './file';

Original answer

You'll want to use module.exports

var hello = function(){
  console.log('hello');
};

module.exports = hello;

If just exporting one thing, I'll usually do it all in one line

var hello = module.exports = function() {
  console.log('hello');
};

Extras

If you use a named function, in the event an error occurs in your code, your stack trace will look a lot nicer. Here's the way I would write it

// use a named function               ↓
var hello = module.exports = function hello() {
  console.log("hello");
};

Now instead of showing anonymous for the function name in the stack trace, it will show you hello. This makes finding bugs so much easier.

I use this pattern everywhere so that I can debug code easily. Here's another example

// event listeners          ↓
mystream.on("end", function onEnd() {
  console.log("mystream ended");
};

// callbacks                              ↓
Pokemon.where({name: "Metapod"}, function pokemonWhere(err, result) {
  // do stuff
});

If you want to export multiple things, you can use exports directly, but you must provide a key

// lib/foobar.js
exports.foo = function foo() {
  console.log("hello foo!");
};

exports.bar = function bar() {
  console.log("hello bar!");
};

Now when you use that file

var foobar = require("./lib/foobar");

foobar.foo(); // hello foo!
foobar.bar(); // hello bar!

As a final bonus, I'll show you how you can rewrite that foobar.js by exporting a single object but still getting the same behavior

// lib/foobar.js
module.exports = {
  foo: function foo() {
    console.log("hello foo!");
  },
  bar: function bar() {
    console.log("hello bar!");
  }
};

// works the same as before!

This allows you to write modules in whichever way is best suited for that particular module. Yay!