Achieving Inheritance in JavaScript Without extends: Understanding "__proto__" in JS

In JavaScript, inheritance is usually done using the extends keyword in classes. But did you know that you can achieve inheritance without extends? This is possible using the __proto__ property, which links one object to another.

In this blog, we will break down how __proto__ works with super simple examples so that even beginners can understand it!

What is __proto__?

Every JavaScript object has a hidden property called __proto__, which points to the prototype of another object. This is how JavaScript enables prototype-based inheritance.

When you try to access a property/method that’s not in the object, JavaScript follows the prototype chain (__proto__) to find it in its parent. Lets discuss this in details:

Lets understand what happens when you try to access a property which is not defined in the class.

🛠️ Steps Explained in the Flowchart:

1. Check Inside the Object Itself

2. Check Inside the Class Prototype (__proto__)

3. Check Inside Object.prototype

4. Reached null (End of Prototype Chain)

Inheritance Without extends Using __proto__

Let's say we have two classes: Person and Student. Normally, we would write class Student extends Person, but here, we’ll use __proto__ instead.

Step 1: Create Classes

// Here I am creating 2 classes 
class Person {
    constructor(name) {
        this.name = name;
    }
    greet() {
        console.log(`Hello, my name is ${this.name}`);
    }
}
class Student {
    constructor(name, grade) {
        this.name = name;
        this.grade = grade;
    }
    study() {
        console.log(`${this.name} is studying in grade ${this.grade}.`);
    }
}

So far, Person has a method greet(), and Student has a method study(). But Student doesn’t inherit from Person yet.

Step 2: Link Student to Person Using __proto__

We want every student to also have access to greet() from Person.
We can achieve this by setting the prototype of Student.prototype to Person.prototype:

// Overriding the __proto__ property of Student by Person.prototype.
Student.prototype.__proto__ = Person.prototype;

Now, when a Student object tries to access a method that isn’t in Student, JavaScript will look inside Person.

---

Step 3: Create Objects and Test

const student1 = new Student("Amit", 10);

student1.study();  // ✅ Output: Amit is studying in grade 10.
student1.greet();  // ✅ Output: Hello, my name is Amit

What Happened Here?

• student1.study() works because study() is in Student.

• student1.greet() works even though greet() is not in Student, because JavaScript looks inside Person via __proto__.

Now, we have successfully achieved inheritance without using extends! 🚀

---

Example 2: Multi-Level Inheritance Without extends

Let’s go a step further. Suppose we create another class, HighSchoolStudent, which should inherit from Student.

Step 1: Create the Class HighSchoolStudent and Link HighSchoolStudent to Student

class HighSchoolStudent {
    constructor(name, grade, stream) {
        this.name = name;
        this.grade = grade;
        this.stream = stream;
    }

    prepareForExams() {
        console.log(`${this.name} is preparing for final exams in ${this.stream}.`);
    }
}

// overriding HighSchoolStudent prototype to Student's
HighSchoolStudent.prototype.__proto__ = Student.prototype;

HighSchoolStudent will inherit from Student, and indirectly from Person.

Step 3: Create Objects and Test

const highSchoolStudent1 = new HighSchoolStudent("Neha", 12, "Science");

highSchoolStudent1.prepareForExams();  // ✅ Output: Neha is preparing for final exams in Science.
highSchoolStudent1.study();            // ✅ Output: Neha is studying in grade 12.
highSchoolStudent1.greet();            // ✅ Output: Hello, my name is Neha.

🎯 How Prototype Chain Works Here
When we call highSchoolStudent1.greet(), JavaScript searches:

HighSchoolStudent → Student → Person → Object.prototype → null

Since greet() is found inside Person, JavaScript calls it successfully!

---

Checking the Prototype Chain

If you want to check the prototype links, use this:

console.log(HighSchoolStudent.prototype.__proto__ === Student.prototype); // ✅ true
console.log(Student.prototype.__proto__ === Person.prototype); // ✅ true
console.log(Person.prototype.__proto__ === Object.prototype); // ✅ true
console.log(Object.prototype.__proto__ === null); // ✅ true

This confirms that JavaScript follows the prototype chain step by step.

Conclusion

✅ We achieved inheritance without using extends, just like JavaScript does behind the scenes.
✅ __proto__ allows us to manually link one class to another.
✅ JavaScript follows the prototype chain to find missing methods.

Now that you understand how extends works internally, try using __proto__ in your own projects!