prototype and __proto__

prototype and __proto__ diagram

concept
prototype is a function attribute (Each function has a prototype property), this property is a pointer to an object. It is a prototype of an object to modify the properties.
__proto__It is an object that has a built-in property, the internal JS use the search attribute prototype chain. Related to the environment with the browser, IE can not access

var Person = function(){};
var p = new Person();

Creating an object above, subjected to three-step
(1) var p = {} ; that is, the initialization of an object P
(2) p.__proto__= Person.prototype;
(. 3)Person.call(p)

p.__proto__ === Person.prototype //true

Remember
prototype constructor is a unique property;

Object __prototype__prototype Properties constructor which normally correspond to each other;

All the prototype Object.prototype constructor method (except Object.prototype itself)

ES6 Class prototype property and property __proto__

Class constructor as syntactic sugar, while the prototype property and __proto__property, so there are two simultaneous inheritance chain.

(1) sub-class __proto__attribute indicating inheritance constructor always points to the parent class.

(2) _ subclass prototype property _proto__attribute indicates inherited methods, always points to the parent class prototype property.

class A {
}

class B extends A {
}

B.__proto__ === A // true
B.prototype.__proto__ === A.prototype // true

B is a subclass __proto__attribute points to the parent class A, class B prototype property of a sub- __proto__attribute points A prototype property of the parent class.

This results because the class inheritance is implemented according to the following mode.

class A {
}

class B {
}

// B的实例继承A的实例
Object.setPrototypeOf(B.prototype, A.prototype);

// B继承A的静态属性
Object.setPrototypeOf(B, A);

"Extended object" chapter is given over to achieve Object.setPrototypeOf methods.

Object.setPrototypeOf = function (obj, proto) {
  obj.__proto__ = proto;
  return obj;
}

Object.setPrototypeOf(B.prototype, A.prototype);
// 等同于
B.prototype.__proto__ = A.prototype;

Object.setPrototypeOf(B, A);
// 等同于
B.__proto__ = A;

This inheritance two chains can be understood: as an object, prototype (the __proto__ properties) subclass (B) is the parent class (A); as a constructor, prototype (prototype attributes) subclass (B) is examples of the parent class.

Object.create(A.prototype);
// 等同于
B.prototype.__proto__ = A.prototype;