function Human(name, age, sex){
   this.name = name;
   this.age = age;
   this.sex = sex;
}
 
Human.prototype.toString = function() {
  return this.name + " is " + this.age + " years old";
}

function Superman(name, age, power) {
  this.name = name;
  this.age = age;
  this.power = power;
}
Superman.prototype = new Human();
Superman.prototype.showPower = function() {
  return "Superman can " + this.power;
}

var superMan = new Superman('Clark Kent', 30, 'fire laser beam');
/*
Clark Kent is 30 years old
Superman can fire laser beam
*/
console.log(superMan.toString());
console.log(superMan.showPower());