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JS Polymorphism

Polymorphism is a core concept in object-oriented programming (OOP) that refers to the ability of objects to take on multiple forms or behaviors based on their context or the type of data they hold. In JavaScript, polymorphism is achieved through method overriding and dynamic method resolution.

Method Overriding:

  • Method overriding is the process of defining a method in a subclass that has the same name and signature as a method in its superclass.
  • When an overridden method is called on an object of the subclass, the subclass’s method implementation is executed instead of the superclass’s method.
					// Parent class (superclass)
class Animal {
    speak() {
console.log("Animal makes a sound.");

// Child class (subclass) inheriting from Animal
class Dog extends Animal {
    speak() {
console.log("Dog barks loudly.");

// Creating instances of the classes
let animal = new Animal();
let dog = new Dog();

// Polymorphic behavior
// Output: Animal makes a sound.
// Output: Dog barks loudly.


Key Concepts:

  • Common Interface:
      • Polymorphism relies on a common interface (e.g., method name and signature) shared by multiple classes or objects.
  • Method Overriding:

    • Subclasses provide their own implementation of methods inherited from their superclass, allowing objects of different subclasses to behave differently when the same method is called.
  • Dynamic Method Resolution:

    • In JavaScript, method resolution occurs dynamically at runtime based on the actual type of the object. This allows for flexible and dynamic behavior based on the context.

Benefits of Inheritance:

  • Code Reusability:
      • Polymorphism enables the reuse of common interfaces and behaviors across different classes, reducing code duplication and promoting modularity
  • Flexibility and Extensibility:

    • Polymorphic behavior allows for flexible and dynamic behavior based on the context or type of object, making it easier to extend and customize classes without modifying existing code.
  • Simplified Code:

    • Polymorphism simplifies code by allowing objects of different types to be treated uniformly through a common interface, leading to cleaner and more maintainable code.


  • Polymorphism can sometimes lead to unexpected behavior if not implemented carefully, especially when dealing with complex class hierarchies and inheritance chains.
  • Overuse of polymorphism can make code harder to understand and debug, especially for developers unfamiliar with the codebase.