JavaScript Constructor Method

A JavaScript constructor method is a special type of method which is used to initialize and create an object. It is called when memory is allocated for an object.

Points to remember

• The constructor keyword is used to declare a constructor method.
• The class can contain one constructor method only.
• JavaScript allows us to use parent class constructor through super keyword.

Constructor Method Example

Let's see a simple example of a constructor method.

1. <script>  
2. class Employee {  
3.   constructor() {  
4.     this.id=101;  
5.     this.name = "Martin Roy";  
6.   }   
7. }  
8. var emp = new Employee();  
9. document.writeln(emp.id+" "+emp.name);  
10. </script>  

Output:

101 Martin Roy

Constructor Method Example: super keyword

The super keyword is used to call the parent class constructor. Let's see an example.

1. <script>  
2. class CompanyName  
3. {  
4.   constructor()  
5.   {  
6.     this.company="Javatpoint";  
7.   }  
8. }  
9. class Employee extends CompanyName {  
10.   constructor(id,name) {  
11.    super();  
12.     this.id=id;  
13.     this.name=name;  
14.   }   
15. }     
16. var emp = new Employee(1,"John");  
17. document.writeln(emp.id+" "+emp.name+" "+emp.company);  
18. </script>  

Output:

1 John Javatpoint

Note - If we didn't specify any constructor method, JavaScript use default constructor method.