Pure prototypial inheritance in JS.

example.js

const SkinnedMesh = THREE.Mesh.extend({
  new: function SkinnedMesh(geometry, materials) {
    var self = THREE.Mesh.new.apply(SkinnedMesh, arguments);
    // initialize instance properties
    self.identityMatrix = THREE.Matrix4.new();
    self.bones = [];
    self.boneMatrices = [];
    return self;
  },
  update: function(camera) {
    ...
    // call base version of same method
    THREE.Mesh.update.call(this);
  }
});

selfish.js

/* vim:set ts=2 sw=2 sts=2 expandtab */
/*jshint undef: true es5: true node: true devel: true evil: true
         forin: true latedef: false supernew: true */
/*global define: true */


"use strict";

Object.prototype.new = function new() {
  return new this.constructor();
};
Object.prototype.extend = function extend(properties) {
  var constructor = new Function(), descriptor = {};
  properties = properties || {};
  Object.getOwnPropertyNames(properties).forEach(function(name) {
    descriptor[name] = Object.getOwnPropertyDescriptor(properties, name);
  });
  descriptor.constructor = { value: constructor };
  return Object.freeze(constructor.prototype = Object.create(this, descriptor));
};

Object.new = function new() {
  return Object.prototype.new();
};
Object.extend = function extend(properties) {
  return Object.prototype.extend(properties);
};