3D Game Programming

functionMovie(title, stars) {

this.title = title;

this.stars = stars;

this.year = (newDate()).getFullYear();

}

This is just a normal function using the function keyword, a name Movie, and a

list of parameters (such as the movie title and the list of stars in the movie).

However, we do something different inside the object builder’s function defi-

nition than what we would normally do for functions. Instead of performing

calculations or changing values, we assign the current object’s properties. In

this case, we assign the current object’s title in this.title, the names of the actors

and actresses who starred in the movie, and even the year in the list of

properties.

Aside from assigning the this values, there really is nothing special about this

function. So how does it create objects? What makes it an object constructor

and not a regular function?

The answer is something we saw in the very first chapter of this book: the

new keyword. We don’t call Movie() the way we would a regular function. It’s an

object constructor, so we construct new objects with it by placing new before

the constructor’s name.

varkung_fu_movie =newMovie('Kung Fu Panda', ['Jack Black','Angelina Jolie']);

The Movie() in new Movie is the constructor function we defined. It needs two

parameters: the title (Kung Fu Panda), and a list of stars (Jack Black and

Angelina Jolie).

Then, thanks to the property assignments we made in the constructor func-

tion, we can access these properties just like we did with our previous objects.

console.log(kung_fu_movie.title);

// => Kung Fu Panda

console.log(kung_fu_movie.stars);

// => ['Jack Black', 'Angelina Jolie']

console.log(kung_fu_movie.year);

// => 2013

You might notice that the year of the Kung Fu Panda movie is wrong (it came

out in 2008). This is because our constructor only knows to set the year

property to the current year. If you are up for a challenge, change the con-

structor so that it takes a third argument—the year. If the year is set, then

use that instead of the current year in the constructor.

report erratum • discuss

Constructing New Objects • 163

Prepared exclusively for Michael Powell