Why null doesn't work in .prototype of constructor

January 29, 2024

I am currently learning JavaScript on javascript.info and I came across this statement:

Link to the statement:
statement
But when I try this code with null in .prototype of constructor:

function Rabbit() {
    this.name = 'rabbit';
}

Rabbit.prototype = null; // *

let obj = new Rabbit();

console.log(Object.getPrototypeOf(obj)); // [Object: null prototype] {}

I get Object.prototype as a [[Prototype]] of instance and not null.
And actually it works for every value if it’s not object, for example here [[Prototype]] of obj will be also Object.prototype:

function Rabbit() {
    this.name = 'rabbit';
}

Rabbit.prototype = 5; // *

let obj = new Rabbit();

console.log(Object.getPrototypeOf(obj)); // [Object: null prototype] {}

And when I have object .prototype it works as it should:

function Rabbit() {
    this.name = 'rabbit';
}

Rabbit.prototype = {
    eats: true,
}; // *

let obj = new Rabbit();

console.log(Object.getPrototypeOf(obj)); // { eats: true }

So why it works like that? Am I wrong and don’t understand something?

>Solution :

Setting any value of .prototype property of a constructor function other than an object automatically sets Object.prototpe as the prototype of the resulting object when the constructor functions is called with new keyword.

From MDN – Function: prototype:

If the prototype of a function is reassigned with something other than an Object, when the function is called with new, the returned object’s prototype would be Object.prototype instead. (In other words, new ignores the prototype property and constructs a plain object.)