javascript objects : create, clone, get/set

jo.js

"use strict";
var util = require('util');
var clone = require('clone');

function inspect(o) {
  console.log(util.inspect(o));
}

function clone1(o) {
  var n = {};
  var d;
  for(var p in o) {
    if (o.hasOwnProperty(p)) {
      d = Object.getOwnPropertyDescriptor(o, p);
      Object.defineProperty(n, p, d);
    }
  }
  return n;
}

// ES6 class
var X = class {
  constructor(x) {

    // data property
    this._x = x;
    // function
    this.f = function() {
      console.log('X::f');
    };
  };

  // getter/setter
  get x()  { return this._x; }
  set x(v) { this._x = v; }
};

// legacy object creation by constructor function
var Y = function(x) {
  if (this instanceof Y) {
    // data property
    this._x = x;

    // function
    this.f = function() {
      console.log('Y::f');
    };

    // getter/setter
    Object.defineProperties(this, {
        "x" : {
          enumerable: true,
          set: function(v) {this._x = v;},
          get: function()  {return this._x;}
        }
      }
    );
  }
  else {
    return new Y(x);
  }
};

// object literal with getter/setter
var Z = {
  // data property
  _x : 1,
  // function
  f  : function() {
        console.log('Z::f');
      },
  // getter/setter
  get x()  {return this._x;},
  set x(v) {this._x = v;}
};


// object literal without getters/setters
var Q = {
  // data property
  _x : 1,

  // function
  f : function() {
    console.log('Q::f');
  },

  // getter/setter
  x  : function(v) {
    if (v) {
      this._x = v;
    }
    return this._x;
  }
};

console.log('X');
var a = new X(1);
a.f();
inspect(a);

console.log('Y');
var b = new Y(1);
b.f();
inspect(b);

console.log('Z');
var c = Z;
c.f();
inspect(c);

console.log('clone');
var d = clone(b);
var e = clone1(b);
inspect(b);
inspect(d);
inspect(e);

console.log('Q');
var q = Q;
inspect(q);
q.f();
var r = clone(q);
inspect(r);
r.x(2);
inspect(r);
console.log(r.x());