Page 143 - this statement

londel26 · May 9th, 2011, 05:02 PM

I am kind of confused about the this in the beginning object function CustomerBookings. I do understand that there is the Object and an instance of an Object and all of that, and for the most part, understand most of the code... But the this in this line for example from below.

Code:

    this.customerName = customerName;

Could someone break it down to me. I have read a couple of books, but it's not fully explained by glossed over. I am one that can't move on until I get this.

Thanks

Code:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Chapter 5: Example 8</title>
</head>
<body>

<h2>Summary of bookings</h2>

<script type="text/javascript">

// CustomerBooking type

function CustomerBooking(bookingId, customerName, film, showDate)
{
    this.customerName = customerName;
    this.bookingId = bookingId;
    this.showDate = showDate;
    this.film = film;
}

CustomerBooking.prototype.getCustomerName = function()
{
    return this.customerName;
}

CustomerBooking.prototype.setCustomerName = function(customerName)
{
    this.customerName = customerName;
}

CustomerBooking.prototype.getShowDate = function()
{
    return this.showDate;
}

CustomerBooking.prototype.setShowDate = function(showDate)
{
    this.showDate = showDate;
}

CustomerBooking.prototype.getFilm = function()
{
    return this.film;
}

CustomerBooking.prototype.setFilm = function(film)
{
    this.film = film;
}

CustomerBooking.prototype.getBookingId = function()
{
    return this.bookingId;
}

CustomerBooking.prototype.setBookingId = function(bookingId)
{
    this.bookingId = bookingId;
}

// Cinema type

function Cinema() 
{
   this.bookings = new Array();
}

Cinema.prototype.addBooking = function(bookingId, customerName, film, showDate) 
{
   this.bookings[bookingId] = new CustomerBooking(bookingId, 
                                                  customerName, film, showDate);
}

Cinema.prototype.getBookingsTable = function() 
{
    var booking;
    var bookingsTableHTML = "<table border=1>";

    for (booking in this.bookings)
    {
        bookingsTableHTML += "<tr><td>";
        bookingsTableHTML += this.bookings[booking].getBookingId();
        bookingsTableHTML += "</td>";

        bookingsTableHTML += "<td>";
        bookingsTableHTML += this.bookings[booking].getCustomerName();
        bookingsTableHTML += "</td>";

        bookingsTableHTML += "<td>";
        bookingsTableHTML += this.bookings[booking].getFilm();
        bookingsTableHTML += "</td>";

        bookingsTableHTML += "<td>";
        bookingsTableHTML += this.bookings[booking].getShowDate();
        bookingsTableHTML += "</td>";
        bookingsTableHTML += "</tr>";
    }
    
    bookingsTableHTML += "</table>";
    return bookingsTableHTML;
}

var londonOdeon = new Cinema();
londonOdeon.addBooking(342, "Arnold Palmer","Toy Story", "15 July 2009 20:15");
londonOdeon.addBooking(335, "Louise Anderson",
                       "The Shawshank Redemption", "27 July 2009 11:25");
londonOdeon.addBooking(566, "Catherine Hughes",
                            "Never Say Never", "27 July 2009 17:55");
londonOdeon.addBooking(324, "Beci Smith","Shrek", "29 July 2009 20:15");


document.write(londonOdeon.getBookingsTable());
</script>

</body>
</html>

jmcpeak · May 9th, 2011, 11:31 PM

Howdy, londel26.

Whenever you see this in code, you can translate that into "this object/instance". When you call the CustomerBooking() function with the new operator, you create a new CustomerBooking object, and the constructor creates properties for that object. So this code:

Code:

this.customerName = customerName;

Can be translated into: "set this CustomerBooking object's (or instance's) customerName property to the value of the customerName parameter." It allows us to reference the current object inside constructor functions and methods. Does that help?

londel26 · May 11th, 2011, 05:18 PM

Ok, so, "this" I guess then would not be a variable or a property, method or otherwise... it's just needed when using objects to state "this" object? And java just needs it because you are talking about an object? And otherwise it does not hold info or do anything other than call, or pull... this specific object. And, if I understand right... that if you had two objects... the "this" would only apply to the object we're in at the moment?

I guess what confused me was that we're just now creating the object, so where are we pulling the customerName var from if we just created it. But I guess that is the point? We're declaring them all at the same time?

Sorry for so many questions.. Just hard for me to move on if I am stuck.. LOL

James

jmcpeak · July 18th, 2011, 09:01 AM

Howdy, londel26.

First, I apologize for this extremely late response. And to answer your first set of questions: yes. You will hear "this" sometimes be referred to "the this variable," but that's only because only saying "this" can get a little confusing.

We don't have to create properties all at once, but that's typically what a constructor function does; it constructs the object. So in the case of the CustomerBooking data type, we create the customerName property so that we can keep track of that data and use it whenever we need to.