JavaScript: clona o extiende un objeto

clone-es5.js

/**
 * Creates a deep copy of an object
 * @param  {Any}    from: Source object to clone
 * @param  {Object} dest: (Optional) destination object to merge with
 * @return {Any} The cloned object
 */
var clone = (function() {
  var _toString = Object.prototype.toString;

  function _clone (from, dest, objectsCache) {
    var prop;
    // determines whether @from is a primitive value or a function
    if (from === null || typeof from !== "object") return from;
    // checks if @from refers to an object created previously
    if (_toString.call(from) === "[object Object]") {
      if (objectsCache.filter(function (item) {
        return item === from;
      }).length) return from;
      // keeps reference to created objects
      objectsCache.push(from);
    }
    // determines whether @from is an instance of any of the following constructors
    if (from.constructor === Date || from.constructor === RegExp || from.constructor === Function ||
      from.constructor === String || from.constructor === Number || from.constructor === Boolean) {
      return new from.constructor(from);
    }
    if (from.constructor !== Object && from.constructor !== Array) return from;
    // creates a new object and recursively iterates over its properties
    dest = dest || new from.constructor();
    for (prop in from) {
      // TODO: allow overwrite existing properties
      dest[prop] = (typeof dest[prop] === "undefined" ?
          _clone(from[prop], null, objectsCache) :
          dest[prop]);
    }
    return dest;
  }

  return function (from, dest) {
    var objectsCache = [];
    return _clone(from, dest, objectsCache);
  };

}());

clone.js

/**
 * Creates a deep copy of an object
 * @param  {Any}    from: Source object to clone
 * @param  {Object} dest: (Optional) destination object to merge with
 * @return {Any} The cloned object
 */
var clone = (() => {
  const _toString = Object.prototype.toString;

  function _clone(from, dest, objectsCache) {
    let prop;
    // determines whether @from is a primitive value or a function
    if (from === null || typeof from !== 'object') return from;
    // checks if @from refers to an object created previously
    if (_toString.call(from) === '[object Object]') {
      if (objectsCache.filter((item) => item === from).length) return from;
      // keeps reference to created objects
      objectsCache.push(from);
    }
    // determines whether @from is an instance of any of the following constructors
    if (from.constructor === Date || from.constructor === RegExp || from.constructor === Function ||
      from.constructor === String || from.constructor === Number || from.constructor === Boolean) {
      return new from.constructor(from);
    }
    if (from.constructor !== Object && from.constructor !== Array) return from;
    // creates a new object and recursively iterates over its properties
    dest = dest || new from.constructor();
    for (prop in from) {
      // TODO: allow overwrite existing properties
      dest[prop] = (typeof dest[prop] === 'undefined' ?
          _clone(from[prop], null, objectsCache) :
          dest[prop]);
    }
    return dest;
  }
  
  return (from, dest) => {
    const objectsCache = [];
    return _clone(from, dest, objectsCache);
  };
  
})();

usage.js

function Freeman() {
    this.name = "Gordon Freeman";
    this.character = "Freeman";
    this.game = "Half-Life";
    this.friends = [];
}

var freeman, david;

freeman = new Freeman();

david = {
    name: "David Rivera",
    character: "jherax",
    friends: [],
    languages: new RegExp(/javascript|jquery|c#|sql|java|vb/i),
    greeting: function() { return "Hi, I am " + this.name; },
    info: {
        job: "programmer",
        birth: new Date()
    }
};

//creamos la referencia circular
freeman.friends = [david, "Barney Calhoun"];
david.friends = [freeman, "John Carmack"];

//clonamos el objeto @david
var cloned = clone(david);

//modificamos propiedades del objeto original
david.name = david.name + " (jherax)";
david.friends.push("Jim Rynor");

//vemos que @clone no fue modificado
console.log("original:", david.name, david.friends);
console.log("clonado:", cloned.name, cloned.friends);