where to add functions in javascript class code example

Example 1: javascript class

class ClassMates{
	constructor(name,age){
    	this.name=name;
      	this.age=age;
    }
  	displayInfo(){
    	return this.name + "is " + this.age + " years old!";
    }
}

let classmate = new ClassMates("Mike Will",15);
classmate.displayInfo();  // result: Mike Will is 15 years old!

Example 2: es6 class example

<script>
   class Student {
      constructor(rno,fname,lname){
         this.rno = rno
         this.fname = fname
         this.lname = lname
         console.log('inside constructor')
      }
      set rollno(newRollno){
         console.log("inside setter")
         this.rno = newRollno
      }
   }
   let s1 = new Student(101,'Sachin','Tendulkar')
   console.log(s1)
   //setter is called
   s1.rollno = 201
   console.log(s1)
</script>