Javascript Prototype继承和Object.create（）？

Question

There is something confusing me about prototypes in JS.

Let's suppose I have an object like this :

 let a = { b: 1 }; 

Now, I want to create another object which inherits of the properties of 'a'.

 let obj = Object.create(a); 

So in this situation, I will link the proto of my 'obj' to the proto of 'a' which will link to the Object.prototype. The first question is, does it remove the link of obj. proto to replace by the a. proto ?

Now let's suppose I do:

 a = 2; 

I would think it updates 'a' in memory removing his references.

So now if I do :

 a.isPrototypeOf(obj) 

It logically returns false . But weirdly 'obj' still point to the property b and can access it(obj.b print 1). What is the mecanism beyond that ?

Answer 1

Technically, when you replace an object with another one new value, the object's old reference will be cut off from the variable. But it will be still alive until the linked variable dies.

var x = { a:10 }
var y = { x };
x = 10;

Now, everyone would think that, y will carry the value 10 with the property x . But that's not, as i said above the x's older memory location will be stay alive until y garbage collected. At the same time, the x would get assigned with newer memory location for the newer value.

So in your case, you are just losing the reference of a by replacing some other value. Hence you cannot use isPrototypeOf(obj) anywhere after replacing the value of a .