What is Polymorphism in JavaScript? Explain It with example.

The polymorphism is a core concept of an object-oriented paradigm that provides a way to perform a single action in different forms. 

It provides an ability to call the same method on different JavaScript objects. 

As JavaScript is not a type-safe language, we can pass any type of data members with the methods.

JavaScript Polymorphism Example 1

Let's see an example where a child class object invokes the parent class method.

1. <script>  
2. class A  
3.   {  
4.      display()  
5.     {  
6.       document.writeln("A is invoked");  
7.     }  
8.   }  
9. class B extends A  
10.   {  
11.   }  
12. var b=new B();  
13. b.display();  
14. </script>  

Output:

A is invoked

Example 2

Let's see an example where a child and parent class contains the same method. Here, the object of child class invokes both classes method.

1. <script>  
2. class A  
3.   {  
4.      display()  
5.     {  
6.       document.writeln("A is invoked<br>");  
7.     }  
8.   }  
9. class B extends A  
10.   {  
11.     display()  
12.     {  
13.       document.writeln("B is invoked");  
14.     }  
15.   }  
16.   
17. var a=[new A(), new B()]  
18. a.forEach(function(msg)  
19. {  
20. msg.display();  
21. });  
22. </script>  

Output:

A is invoked
B is invoked

Example 3

Let's see the same example with prototype-based approach.

1. <script>  
2. function A()  
3. {  
4. }  
5. A.prototype.display=function()  
6. {  
7.   return "A is invoked";  
8. }  
9. function B()  
10. {  
11.     
12. }  
13.   
14. B.prototype=Object.create(A.prototype);  
15.   
16. var a=[new A(), new B()]  
17.   
18. a.forEach(function(msg)  
19. {  
20.   document.writeln(msg.display()+"<br>");  
21. });  
22. <script>  

Output:

A is invoked
B is invoked