Ejercicios

1. ¿Cual es la salida?

   > z
   { x: 3, y: 1 }
   > Object.keys(z)
   ?????
   > Object.keys(z).forEach(function(i) { console.log(i+" -> "+z[i]); })
   ?????
   

2. ¿Que queda finalmente en z?

   > z
   { x: 2, y: 1 }
   > Object.defineProperty(z, 'y', {writable : false})
   { x: 2, y: 1 }
   > z.x = 3
   ??????
   > z.y = 2
   ??????
   > z
   

3. ¿Cuales son las salidas?

   > obj = { x : 1, y : 2}
   { x: 1, y: 2 }
   > bValue = 5
   5
   > Object.defineProperty(obj, "b", {get: function(){ return bValue; }, 
                                      set: function(y){ bValue = y; }}) 
   { x: 1, y: 2 }
   > obj.b = "hello"
   
   > bValue
   
   > obj.b
   
   > bValue = "world"
   
   > obj.b
   
   >
   

4. ¿Cuales son las salidas?

   > var o = {};
   undefined
   > Object.defineProperty(o, "a", { value : 1, enumerable:true });
   { a: 1 }
   > Object.defineProperty(o, "b", { value : 2, enumerable:false });
   { a: 1 }
   > Object.defineProperty(o, "c", { value : 3 }); // enumerable defaults to false
   { a: 1 }
   > o.d = 4; // enumerable defaults to true when creating a property by setting it
   4
   >  
   undefined
   > for (var i in o) {    
   ...   console.log(i);  
   ... }
   ???????
   > Object.keys(o); 
   ???????
   > o.propertyIsEnumerable('a'); 
   ????
   > o.propertyIsEnumerable('b');
   ????
   > o.propertyIsEnumerable('c');
   ????
   > o.b
   ????
   > o["b"]
   ????
   

5. > function foo(a, b){return a * b;}
   undefined
   > f = function foo(a, b){return a * b;}
   [Function: foo]
   > foo.length
   2
   > foo.constructor
   [Function: Function]
   > foo.prototype
   {}
   > typeof foo.prototype
   'object'
   > [1, 2].constructor
   [Function: Array]
   

6. ¿Cuales son las salidas?

   > Object.getPrototypeOf({ a: 1})
   
   > Object.getPrototypeOf([1,2,3])
   
   > Object.getPrototypeOf([1,2,3]) == Array.prototype
   
   > Object.getPrototypeOf({ a:1 }) === Object.prototype
   
   > Object.getPrototypeOf(Array.prototype)
   
   > Object.getPrototypeOf(Object.prototype)
   
   > Object.getPrototypeOf(function() {})
   
   > Object.getPrototypeOf(Object.getPrototypeOf(function() {}))
   
   > [1,2,3].__proto__
   
   > [1,2,3].__proto__ == Array.prototype
   

Figura: Jerarquía de Prototipos Nativos

var b = new Foo(20);
var c = new Foo(30);

Figura 61.2: __proto__ and prototypes