Prototypes

Question 1

Prototype

Answer 1

In JavaScript, objects have a special hidden property [[Prototype]] that is either null or references another object. The property [[Prototype]] is internal and hidden. You can set it using __proto__

Question 2

Example

Answer 2

let animal = {
eats: true
};
let rabbit = {
jumps: true
};

rabbit.__proto__ = animal;
So if animal has a lot of useful properties and methods, then they become automatically available in rabbit. Such properties are called “inherited”.
rabbit inherits from animal, that inherits from Object.prototype (because animal is a literal object {…}, so it’s by default), and then null above it:

Question 3

Value of this

Answer 3

No matter where the method is found: in an object or its prototype. In a method call, this is always the object before the dot.

Question 4

for .. in loop

Answer 4

The for..in loop iterates over inherited properties too.

Question 5

Enumerable properties

Answer 5

Like all other properties of Object.prototype, it has enumerable:false flag. And for..in only lists enumerable properties. That’s why it and the rest of the Object.prototype properties are not listed.