Наследование копированием свойств

Inheritance properties

/* Поверхностное копирование */
function extend(parent, child) {
  var i;
  child = child || {};
  for (i in parent) {
    if(parent.hasOwnProperty(i)) {
      child[i] = parent[i];
    }
  }
  return child;
}

var dad = { name: "Adam" };
var kid = extend(dad);
kid.name; // "Adam";

//
var dad = {
  counts: [1, 2, 3],
  reads: {paper: true},
};
var kid = extend(dad);
kid.counts.push(4);
dad.counts.toString(); // "1, 2, 3, 4"
dad.reads === kid.reads; // true


/* Полное копирование */
function extendDeep(parent, child) {
  var i,
      toStr = Object.prototype.toString,
      astr = "[object Array]";
      
  child = child || {};
  
  for (i in parent) {
    if(parent.hasOwnProperty(i)) {
      if(typeof parent[i] === "object") {
        child[i] = (toStr.call(parent[i]) === astr) ? [] : {};
        extendDeep(parent[i], child[i]);
      }
      else {
        child[i] = parent[i];
      }
    }
  }
  return child;
}

var dad = {
  counts: [1, 2, 3],
  reads: {paper: true},
};
var kid = extendDeep(dad);

kid.counts.push(4);
kid.counts.toString(); // "1, 2, 3, 4"
dad.counts.toString(); // "1, 2, 3"

dad.reads === kid.reads; // false
kid.reads.paper = false;

kid.reads.web = true;
dad.reads.paper; // true