3D Game Programming

When we use functions in objects like this, we call them with a different name,

method. Methods let us change an object or, as we’re doing here, return some

other information about the object.

Take a look at the aboutMe() method and how we use the this keyword. The this

keyword is how we refer to the current object. If we’d used title instead of

this.title, we would have gotten an error message telling us that title was unde-

fined. In this example, title was undefined because the code was looking for

a variable named title somewhere else in the program. By using this.title, we are

specifying that we want the title property assigned to the current object.

console.log() Is Your Friend

Web programmers use console.log() all the time to double-check that

variables have the value we expect them to have. It never shows

up in the web page or the game, but programmers can see it—and

fix things if they are broken. Just remember to remove console.log()

when you’re done—it is much easier to use the JavaScript console

without a ton of console.log() messages!

17.3 Copying Objects

In real life, you copy a cool idea or thing by copying everything it does and

changing a few things here and there to make it even better. The thing you’re

copying becomes the prototype for the new way of doing it. JavaScript handles

copying objects in a similar way.

To describe another movie, we can copy the prototypical best_movie object by

using Object.create:

vargreat_movie = Object.create(best_movie);

great_movie.aboutMe();

// => Star Wars, starring: Mark Hamill,Harrison Ford,Carrie Fisher

Object.create will create a new object with all the same properties and methods

of the prototypical object we created earlier. So the new object, great_movie, has

the same title and actors as the original best_movie. It also has the same aboutMe()

method.

We don’t need to make any changes to the aboutMe() method. We still want it

to log the movie title and the list of the stars to the JavaScript console. Even

if the title and list of stars changes, the aboutMe() method stays the same—it

may log different information, but it will use the same properties to do so.

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Copying Objects • 161

Prepared exclusively for Michael Powell