Once a singleton always a singleton

included.js

var Thing = require('./thing');

console.log('Include thing from another file');
console.log(Thing.thing, ":thing in included");

main.js

var Thing = require('./thing');

console.log(Thing.thing, ": thing in main");

Thing.setSomething();

console.log(Thing.thing, ":thing in main");
require('./included');

thing.js

// Thing.thing gets cached after the first require
// As long as the data is set early on, all subsequent requires
// will have access to it.
module.exports = {
  setSomething: function() {
    console.log('set Thing.thing');
    module.exports.thing = 5;
  },
  thing: undefined
};