// Constructor function function Person(name, age, gender) { this.name = name; this.age = age; this.gender = gender; this.talk = function () { alert(this.name + ' says Hello! \n I\'m ' + this.age); } } Person.prototype.reduceAge = function(by){ this.age = this.age-by; } var personA = new Person('Adam', 30, 'Male'); // instance of Person var personB = new Person('Eve', 29, 'Female'); // another instance of person personA.reduceAge(2); // would reduce the age by 2. eg: 30-2=28; personA.talk(); // Will alert "Adam says Hello! I'm 28" personB.talk(); // Will alert "Eve says Hello! I'm 29"