Just a simple demo of prototype chaining & inheritance I find useful.

protoPerson

function Person(firstName, lastName){
    this.firstName = firstName;
    this.lastName = lastName;
};

Person.prototype.getFullName = function(){
    return this.firstName + " " + this.lastName;
};

function Employee(firstName, lastName, position){
    Person.call(this, firstName, lastName);  //inherits properties from Person()
    this.position = position;
};

Employee.prototype = new Person(); //Inherits Person() prototype
Employee.prototype.getFullName = function() {
    var fullName = Person.prototype.getFullName.call(this); //calling line 6 as if it were an Employee()  
    return fullName + ", " + this.position;
};

var employee = new Employee("Foo", "Boy", "Pain Enhancer");

alert(employee.getFullName() );