example.js

function MedievalSoldier(type, weapon, attack) {
  //properties:
  this.type = type;
  this.weapon = weapon; // some type of modifer 
  this.damage = 5;
  this.level = 1;
  //methods:
  this.attack = null;
}
var mySolider = new MedievalSoldier("pikeman", "spear");

mysolider.protype.attack  = function(){
  return {
    damage: 5 * (this.level + this.damage);
  }
}