为什么 jQuery 的深层复制不复制描述性属性？

Question

While learning about Object.defineProperty() , I was trying it for deep cloned objects. Consider the following snippet,

 var obj = {}; Object.defineProperty(obj, 'key', { get: () => {return key}, set: (value) => { if (typeof(value) == 'number'){ key = value; } } }); obj.key = 54; console.log(obj.key); // Output: 54 obj.key = ['a', 'b']; console.log(obj.key); // Output: 54 var clone = $.extend(true, {}, obj); clone.key = 44; console.log(obj.key, clone.key); // Output: 54 44 clone.key = 'hello'; console.log(clone.key); // Output: hello

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Why does the clone created by jQuery not maintain the original getters and setters from the object. If I do require this functionality, how can I get deeply cloned objects to have the same getters and setters as their parents?

Answer 1

When you define a property using Object.defineProperty , with a descriptor for set , you add an event for the value to be changed. This event is associated with the reference of object.

When you use $.extend , what it does is, copy its value.

Following is the partial code of $.extend

for (; i < length; i++) {

  // Only deal with non-null/undefined values
  if ((options = arguments[i]) != null) {

    // Extend the base object
    for (name in options) {
      src = target[name];
      copy = options[name];

As you see, only the value is copied. The reason why the descriptor is not copied can be that, the intention of having a descriptor would be specific to that object alone and not to its child.

This behavior is also shared by Object.assign

 var obj = {}; Object.defineProperty(obj, 'key', { get: () => { return key }, set: (value) => { if (typeof(value) == 'number') { key = value; } } }); obj.key = 54; console.log(obj.key); // Output: 54 obj.key = ['a', 'b']; console.log(obj.key); // Output: 54 var clone = Object.assign({}, obj) clone.key = 44; console.log(obj.key, clone.key); // Output: 54 44 clone.key = 'hello'; console.log(clone.key); // Output: hello

Answer 2

I think the problem is the scope of the functions. You are not able to clone the scope and to avoid problems they decided to omit functions while cloning.

But i am not sure about that.