gistfile1.js

// base.js:

function PluginBase() {
    this.something = 1
}

PluginBase.prototype.something = function () {
    console.log("in base class")
}

exports.PluginBase = PluginBase


/////////////////////////////////
// plugin.js

var inherit = require('util').inherits
var PluginBase = require('./base.js').PluginBase

inherit(Plugin, PluginBase)
function Plugin() {
    console.log("constructor")
}

Plugin.prototype.some_method = function() {
    console.log("in loaded plugin")
    this.something()
}

exports.Plugin = Plugin


//////////////////////////////////////////////////
// test.js

var Plugin = require('./plugin').Plugin

var instance = new Plugin()
instance.some_method()  // in loaded plugin
instance.something()    // in base class