🧩 Prototypes & Prototype Chain in JavaScript (OOP)

Last Updated: 25th October 2025

  • Every object in JavaScript is connected to another object called its prototype.
  • The prototype acts as a blueprint or parent that shares properties and methods with its child objects.
  • Each JS object has a hidden property called [[Prototype]] (accessible by __proto__).
  • It points to another object (the prototype).
  • If JS doesn’t find a property/method in the object, it looks for it in the prototype.

Hinglish Tip 🗣: Prototype ko ek “parent object” samjho — jisse child object features (properties/methods) inherit karta hai.

Example:

const person = {
  greet() {
    console.log("Hello!");
  },
};

const student = {
  name: "Sachin",
};

// Linking student → person
student.__proto__ = person;

student.greet(); // Output: Hello!

👉 Here, student doesn’t have greet(), so JS looks in person (its prototype).

📚 Prototype Chain

The process of looking up a property/method in parent prototypes is called the Prototype Chain.

It continues until:

  • The property is found, OR
  • It reaches the top of the chain → Object.prototype (which has methods like toString(), hasOwnProperty(), etc.)
  • JS searches → child → parent → grandParent → Object.prototype

Example:

const grandParent = {
  sayHi() {
    console.log("Hi from GrandParent!");
  },
};

const parent = Object.create(grandParent);
const child = Object.create(parent);

child.sayHi(); // Output: Hi from GrandParent!

Hinglish Tip 🗣: Chain me upar tak search hota hai jab tak mil nahi jata — isiliye ise “prototype chain” kehte hain.

💡 Quick Practice

  • Create a prototype object animal with eat() method and make dog inherit it.
  • Use Object.create() to chain 3 levels (child → parent → grandparent).
  • Add a method to constructor’s prototype and access it from two instances.
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