Sub.prototype --> Base.prototype --> Object.prototype --> null var sub = new Sub({ a: 1, b: 2 }); ```

关于 Object.defineProperty

The Object.defineProperty() method defines a new property directly on an object, or modifies an exisiting property on an object, and returns the object.

js Object.defineProperty(obj, prop, descriptor);

• obj The object on which to define the property.
• prop The name of the property to be defined or modified.
• descriptor The descriptor for the property being defined or modified.
  • configurable 是否可删除目标属性或修改属性以下特性 (writable|configurable|enumerable)
  • enumerable 是否能在 for-in 循环中遍历出来或在 Object.keys 中列举出来
  • value
  • get
  • set
• return The object that was passed to the function.

上面不想翻译了，详见 MDN Web Docs 。

借助 Object.defineProperty 的一个伪的双向绑定实现：

```js const model = {}; const view = document.createElement('input');

Object.defineProperty(model, 'value', { get: function() { return this.value; }, set: function(val) { this.value = val; view.value = val; }, });

view.addEventListener('change', function(e) { model.value = e.target.value; });

document.body.appendChild(view); ```

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