访问 `__proto__` 属性并没有得到我期望的 Javascript

Question

所以，我试图理解这段代码：

function Mammal() {
  this.isMammal = 'yes';
}

function MammalSpecies(sMammalSpecies) {
  this.species = sMammalSpecies;
}

MammalSpecies.prototype = new Mammal();
MammalSpecies.prototype.constructor = MammalSpecies;

var oCat = new MammalSpecies('Felis');
console.log(oCat.isMammal); // 'yes'

function Animal() {
  this.breathing = 'yes';
}

var test = Object.getPrototypeOf(Object.getPrototypeOf(oCat))
console.log("Mark:1", test) /* output
{constructor: ƒ}
constructor: ƒ Mammal()
__proto__: Animal
breathing: "yes"
__proto__: Object*/
console.log("Mark:1.3", test.__proto__) /* output
{constructor: ƒ, __defineGetter__: ƒ, __defineSetter__: ƒ, hasOwnProperty: ƒ, __lookupGetter__: ƒ, …}
constructor: ƒ Object()
hasOwnProperty: ƒ hasOwnProperty()
isPrototypeOf: ƒ isPrototypeOf()
propertyIsEnumerable: ƒ propertyIsEnumerable()
toLocaleString: ƒ toLocaleString()
toString: ƒ toString()
valueOf: ƒ valueOf()
__defineGetter__: ƒ __defineGetter__()
__defineSetter__: ƒ __defineSetter__()
__lookupGetter__: ƒ __lookupGetter__()
__lookupSetter__: ƒ __lookupSetter__()
get __proto__: ƒ __proto__()
set __proto__: ƒ __proto__()
*/
console.log("Mark:2", Object.getPrototypeOf(test)) /* output
{constructor: ƒ, __defineGetter__: ƒ, __defineSetter__: ƒ, hasOwnProperty: ƒ, __lookupGetter__: ƒ, …}
constructor: ƒ Object()
hasOwnProperty: ƒ hasOwnProperty()
isPrototypeOf: ƒ isPrototypeOf()
propertyIsEnumerable: ƒ propertyIsEnumerable()
toLocaleString: ƒ toLocaleString()
toString: ƒ toString()
valueOf: ƒ valueOf()
__defineGetter__: ƒ __defineGetter__()
__defineSetter__: ƒ __defineSetter__()
__lookupGetter__: ƒ __lookupGetter__()
__lookupSetter__: ƒ __lookupSetter__()
get __proto__: ƒ __proto__()
set __proto__: ƒ __proto__()
(same as test.__proto__)
*/

function Mammal() {
  this.isMammal = 'yes';
}

function MammalSpecies(sMammalSpecies) {
  this.species = sMammalSpecies;
}

MammalSpecies.prototype = new Mammal();
MammalSpecies.prototype.constructor = MammalSpecies;

var oCat = new MammalSpecies('Felis');
console.log(oCat.isMammal); // 'yes'

function Animal() {
  this.breathing = 'yes';
}

var test = Object.getPrototypeOf(Object.getPrototypeOf(oCat))
console.log("Mark:1", test)
/* output
{constructor: ƒ}
constructor: ƒ Mammal()
__proto__: Animal
breathing: "yes"
__proto__: Object*/
console.log("Mark:1.3", test.__proto__)
/* output
{constructor: ƒ, __defineGetter__: ƒ, __defineSetter__: ƒ, hasOwnProperty: ƒ, __lookupGetter__: ƒ, …}
constructor: ƒ Object()
hasOwnProperty: ƒ hasOwnProperty()
isPrototypeOf: ƒ isPrototypeOf()
propertyIsEnumerable: ƒ propertyIsEnumerable()
toLocaleString: ƒ toLocaleString()
toString: ƒ toString()
valueOf: ƒ valueOf()
__defineGetter__: ƒ __defineGetter__()
__defineSetter__: ƒ __defineSetter__()
__lookupGetter__: ƒ __lookupGetter__()
__lookupSetter__: ƒ __lookupSetter__()
get __proto__: ƒ __proto__()
set __proto__: ƒ __proto__()
*/
console.log("Mark:2", Object.getPrototypeOf(test))
/* output
{constructor: ƒ, __defineGetter__: ƒ, __defineSetter__: ƒ, hasOwnProperty: ƒ, __lookupGetter__: ƒ, …}
constructor: ƒ Object()
hasOwnProperty: ƒ hasOwnProperty()
isPrototypeOf: ƒ isPrototypeOf()
propertyIsEnumerable: ƒ propertyIsEnumerable()
toLocaleString: ƒ toLocaleString()
toString: ƒ toString()
valueOf: ƒ valueOf()
__defineGetter__: ƒ __defineGetter__()
__defineSetter__: ƒ __defineSetter__()
__lookupGetter__: ƒ __lookupGetter__()
__lookupSetter__: ƒ __lookupSetter__()
get __proto__: ƒ __proto__()
set __proto__: ƒ __proto__()
(same as test.__proto__)
*/

所以，我不明白的是，我希望 test.__proto__ 等于：

breathing: "yes"
__proto__: Object

因为test对象的__proto__键等于那个，如“Mark:1”日志所示，对吧？ Object.getProtoTypeOf(test) 记录相同。我错过了什么？

Answer 1

让我们看看下一行。

Object.getPrototypeOf(Object.getPrototypeOf(oCat))

Object.getPrototypeOf(oCat) 是new Mamal()。

所以我们可以说Object.getPrototypeOf(Object.getPrototypeOf(oCat)) 等于Object.getPrototypeOf(new Mamal())。

而Object.getPrototypeOf(new Mamal()) 是Mamal，因为new Mamal() 返回一个原型为Mamal 的新对象。

这就是为什么在调用console.log("Mark:1", test) 时会看到Mamal。