The Roots of Every Object

In JavaScript, every object has a hidden property called [[Prototype]]. It either equals null, or it references another object — that other object is called its prototype.

When you read a property from an object and it doesn't exist there, JavaScript automatically searches for it up the prototype chain.

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

Object.setPrototypeOf(rabbit, animal); // set animal as rabbit's prototype

console.log(rabbit.jumps); // true — rabbit's own property
console.log(rabbit.eats);  // true — found in animal (the prototype)!

Inheritance is read-only: writing rabbit.eats = false creates a new own property on rabbit and does NOT change animal.