Function is instance of Object, and Object is instance of Function?

Question

 console.log(Function instanceof Object);//true
 console.log(Object instanceof Function);//true

This code is taken from article : https://github.com/stevekwan/experiments/blob/master/javascript/object-vs-function.html

I guess I understand what is prototypal inheritance and how Js object model works, but this circular links between two basic hmm.. probably constructors(which is functions which is objects .. and all objects are instance of Object constructor...) Function and Object just blow my mind.

In class-oriented languages i can imagine that there is some basic class Object, and every class i make is automatically inherits from it.

For me there is time consistency - class Object appears at first, then everything else i wrote appears at second etc. I don't really understand how two constructors magically appear at the same time and are instances of each other.

Answer 1

Note that Function and Object are both global symbols that refer to functions. So both of those functions are instances of both Object and Function, because they inherit from both prototypes.

It's less confusing if you do this:

var a = Function, b = Object;

console.log(a instanceof Object);
console.log(b instanceof Object);
console.log(a instanceof Function);
console.log(b instanceof Function);

Those functions have those properties just like any other function does:

var c = function() {};

console.log(c instanceof Object);
console.log(c instanceof Function);

On the left-hand side of the instanceof operator, all that matters is the nature of the object involved.

Answer 2

There is no circularity. There can't be cycles in [[Prototype]] chains.

Function instanceof Object means that the [[Prototype]] chain of Function contains Object.prototype.

Object instanceof Function means that the [[Prototype]] chain of Object includes Function.prototype.

It's not circular because Object is not in the [[Prototype]] chain of Object.prototype and Function is not in the [[Prototype]] chain of Function.prototype.

The [[Prototype]] chains are

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╎ Function ━┓       /* Function instanceof Object */         ╎
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╎           ┣━━❯ Function.prototype ━━━━━❯ Object.prototype ━━━❯ null
╎           ┃                        ╎ ╰╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╯
╎           ┃                        ╰╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╮
╎ Object ━━━┛       /* Object instanceof Function */         ╎
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