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Welcome back, Ashley here.

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Let's move forward with our library app.

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So far we've declared three classes,
library, book and

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patron, each one in their own js file.

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When I'm building out an object oriented
app, I like to follow my rough plan and

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build out my constructor methods for
each class first.

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As a quick recap a constructor method is
where we tell the class, the properties.

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And the property's initial
values that any new object

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of that class type should
have available to them.

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Building the constructor methods first
let's me instantiate a few test objects

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right off the bat.

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That I can plug some data into and
play with as I go.

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This gives me a way to make sure that my
code is working properly along the way.

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So that's what we'll be doing next.

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Building out the constructor methods for
the library, book and patron classes.

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Let's start with the library class.

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To recap, according to our rough plan,
the library class has two properties,

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books and patrons.

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These are going to be initialized to
empty arrays in our constructor method.

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That's because the library
doesn't have any books or

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patrons yet, it's a clean slate.

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A user of our library
system can add books and

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patrons to these arrays, through
the methods relayed out in our rough.

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AddBook and addPatron.

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This means we don't have to pass
anything into our constructor method for

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the library class.

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As for our book class, we're going
to be initializing a few properties

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in the constructor method as well.

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Just so you know,

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properties don't have to be initialized
inside a constructor method.

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They can be initialized, like any
variable, in a method on a class as well.

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If that's the case,
that means an object of that class type

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will only have those properties
if that method is called on.

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Our rough plan says that the book
class will have the properties for

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title, author and isbn.

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All of these values will
need to be passed in.

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Finally, let's talk
about the patron class.

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The properties initialized in
the constructor method are name,

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email and currentBook.

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The values for the name and

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email properties will be passed in
when a patron object is created.

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In the real world, the patron will be
providing that information to the library

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employee who keys it into the system.

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The currentBook property,
however, is a little different.

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A patron won't have checked out a book
when they are first entered into

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the system.

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So when the new patron object is created,

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the value of the currentBook property
should probably just be null.

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We can set that directly
inside the constructor method

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without passing in a value.

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Later on, when a patron does borrow
a book, the checkOut method can update

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the current book property so it holds
the book that the patron is borrowing.

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Let's add these constructor methods to our
class files, then afterwards we can create

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some test objects and see what they
look like and how they work so far.

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Head to the attached work space to see
the updated read me with new instructions.

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Or see the teachers notes
attached to this video.

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Once you're finished or

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if you're having trouble, check out
the solution following this video.