Q216- What is the prototype chain?

The prototype chain in JavaScript is a mechanism through which objects inherit properties and methods from other objects.
It’s part of JavaScript’s prototype-based inheritance model.

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1️⃣ Every Object Has a Prototype

When you create an object, JavaScript automatically links it to another object called its prototype, from which it can inherit properties or methods.

const person = { greet() { console.log("Hello!"); } };
const user = Object.create(person);

user.greet(); // "Hello!"

Here, user doesn’t have greet(), so JS looks up its prototype (person) — this lookup process forms the prototype chain.

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2️⃣ The Chain Continues Upward

Every object’s prototype itself has a prototype — until it reaches the end of the chain (null).

console.log(Object.getPrototypeOf(user) === person); // true
console.log(Object.getPrototypeOf(person) === Object.prototype); // true
console.log(Object.getPrototypeOf(Object.prototype)); // null (end)

Prototype lookup order: user → person → Object.prototype → null

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3️⃣ Functions Have prototype Property

When you define a function, it automatically gets a prototype property that is used when creating objects via new.

function Animal() {}
Animal.prototype.speak = function () {
  console.log("Animal sound");
};

const dog = new Animal();
dog.speak(); // "Animal sound"

Here, dog inherits speak() from Animal.prototype.

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4️⃣ Prototype Chain Lookup

When accessing a property:

1. JS checks the object itself.
2. If not found, it looks up the prototype chain.
3. Stops when it reaches null.

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Visualization

dog --> Animal.prototype --> Object.prototype --> null

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💡 In Short:

The prototype chain is how JavaScript objects inherit properties and methods from other objects.
It continues upward through prototypes until it reaches Object.prototype, whose prototype is null.