Classes

class Student {
  constructor(name, marks) {
    this.name = name;
    this.marks = marks;
  }

  grade() {
    return this.marks >= 80 ? "A" : this.marks >= 60 ? "B" : "C";
  }
}

class Monitor extends Student {
  grade() {
    return super.grade() + " (monitor)";
  }
}

const ali = new Student("Ali", 85);
const sara = new Monitor("Sara", 72);
console.log(ali.grade(), sara.grade());