When we create an object and look at the [[prototype]] of it, there is a __proto__ property and even further we expand there is the same set of properties with another __proto__ but with the null value.
What is the reason for these two levels of __proto__ and why it is null in the second occurrence?
Wow, that's really confusing. __proto__ is a (deprecated) getter/setter, and expanding it in the console will run the getter on the start of the prototype chain. It then returns Object.protype, and expanding __proto__ on that result object will now result in null.
But my advice is to completely ignore __proto__. It is deprecated and should not be used anywhere, in the console only look at the [[prototype]] which displays the prototype chain links.
Let's take an example to illustrate what happens internally:
Define an ordinary object a const a = {} which is Sugar syntax for const a = new Object()
new operator points a[[prototype]] to Object.prototype. a[[prototype]] = Object.prototype
Object.prototype has a [[prototype]] which value is null
So a[[prototype][[prototype]] => Object.prototype[[prototype]] => null
