[JavaScript] super

class Person {

constructor(name, first, second) {

this.name = name;

this.first = first;

this.second=second;

}

sum() {

return this.first+this.second;

}

}

class PersonPlus extends Person {

constructor(name, first, second, third) {

super(name, first, second);

this.third=third;

}

sum() {

return super.sum()+this.third;

}

avg() {

return (this.first+this.second+this.third)/3;

}

}

var kim = new PersonPlus('kim', 10, 20, 30);

console.log("kim.sum()", kim.sum());

-> kim.sum() 60

console.log("kim.avg()", kim.avg());

-> kim.avg() 20