JavaScript based learning - and shielding property settings

Property of the object

• Modify the properties of the object itself

  var myObject = { a: 2 };
  myObject.a = 3;
  console.log(myObject); // {a: 3}

---

• If A is not a direct presence in myObject, [[the Prototype]] chain will be traversed, if not found in the original chain, it will be added directly to a myObject
  myObject.b =. 3, b is not found in the myObject, to anotherObject look on, can not find, Object object has been found, did not find b, b add properties directly on the myObject

  var anotherObject = { a: 2 };
  var myObject = Object.create(anotherObject);
  myObject.b = 3;
  console.log(myObject); // {b: 3}

shield

[[The Prototype]] If the upper chain appears in a name attribute myObject, there is also that of the shield will occur.
myObject contains a shielding property of a prototype of all upper chain properties.

  var anotherObject = { a: 2 };
  var myObject = Object.create(anotherObject);
  Object.defineProperty(myObject, 'a', { value: 3, writable: true });
  console.log(myObject); // {a: 3}
  console.log(anotherObject); // {a: 2}
  myObject.a = 4;
  console.log(anotherObject); // {a: 2}
  console.log(myObject); // {a: 4}

---

If not present in a myObject, present in the anotherObject, myObject.a = 3, there will be three special cases

1. If [[the Prototype]] the presence of a top chain, and not read (writable: true), then added in an attribute named a myObject, it is the shielding properties.

  var anotherObject = { a: 2 };

  var myObject = Object.create(anotherObject);
  console.log(myObject.a); // 2

  myObject.a = 3;
  console.log(myObject.a); // 3
  console.log(myObject); // {a: 3}
  console.log(anotherObject); // {a: 2}

2. If [[the Prototype]] the presence of the upper strand a, but read-only (writable: false), it can not be added to the myObject a. If strict mode error. But can be defined in definePrototype a.

  // 'use strict'; // Uncaught TypeError: Cannot assign to read only property 'a' of object '#<Object>'
  var anotherObject = {};
  Object.defineProperties(anotherObject, {
    a: {
      writable: false,
      value: 2
    }
  });

  var myObject = Object.create(anotherObject);
  console.log(myObject.a); // 2
  myObject.a = 3;
  console.log(myObject.a); // 2
  console.log(myObject); // {}
  console.log(anotherObject); // {a: 2}

  Object.defineProperty(myObject, 'a', { value: 3 });
  console.log(myObject); // {a: 3}
  myObject.a = 4;
  console.log(myObject); // {a: 4}

3. If in a [[Prototype]] is a top setter, it is not added to the myObect, it will not redefine the setter, but calling this setter

  var anotherObject = {
    get a() {
      return this._a_;
    },
    set a(val) {
      this._a_ = val;
    }
  };

  var myObject = Object.create(anotherObject);
  console.log(myObject); // {}
  myObject.a = 3;
  console.log(myObject); // {_a_: 3}

---

Implicit shield

  var anotherObject = { a: 2 };
  var myObject = Object.create(anotherObject);

  console.log(anotherObject.a); // 2
  console.log(myObject.a); // 2

  // 相当于 myObject = myObject.a + 1
  myObject.a++;

  console.log(anotherObject.a); // 2
  console.log(myObject.a); // 3