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Getters
6:10Create properties with dynamic values using getters in JavaScript.
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Welcome back.
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In JavaScript, there are two special
methods called getters and setters.
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These methods allow us to create and
retrieve or
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update an object's
properties respectively.
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You learned previously how to access or
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update an object's properties
using dot and bracket notation.
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So why do we need methods
that do the same thing?
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I promise that the answer is not
to needlessly complicate things.
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The idea behind getter and
setter methods is to increase flexibility.
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With getter and setter methods,
you have the option to include logic when
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retrieving or setting the value of
a property while still enjoying the simple
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syntax of accessing and
setting these properties directly.
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This concept might be
a little confusing at first.
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So feel free to slow me down if you want
or rewatch this section a few times.
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You'll also get a chance to practice
in a code challenge after this video.
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>> So what is a getter method?
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In JavaScript it's a special
method used when you want to have
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a property that has a dynamic or
computed value.
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The value of the property is
computed in the getter method.
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And even though it's not stored or
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attached to the object it can be
accessed just like a regular property.
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Go ahead and
open up the Pet.js file to follow along.
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Put a few new lines in and
after your constructor method.
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For this example we're going to add a
property called activity to the pet class.
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This property should tell us what our
pet is up to based on the time of day.
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Unfortunately, we can't set that
property in our constructor method,
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because its value is dynamic.
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It changes depending on what time it is.
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This is a perfect opportunity
to use the getter method.
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To create a getter method,
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you type the keyword get and
then the name of the property in question.
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And then just like a regular method,
we add parentheses and then curly braces.
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Inside the curly braces we'll compute and
return our value.
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To figure out the pet's activity, we'll get
the current hour and write an if statement
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that will return a different activity
depending on that hour value.
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I'm going to keep this function
as simple as possible, but
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this is a great opportunity for
you to use your imagination and
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make this function more
interesting by adding more to it.
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First, we wanna figure out
what hour of the day it is.
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And guess what, we're gonna use
a built-in JavaScript object to do this.
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Declare a variable using
the const keyword called today.
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This variable will hold a new instance
of the JavaScript date object.
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Familiar, right?
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If we were to output the value
of the today variable right now,
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we would see a string that tells us
today's date and time in universal time.
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For more information about universal time,
check out the teacher's notes.
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Getting today's date and time as a string
isn't terribly useful for our purposes but
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luckily the date object has many
different methods that will return
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pieces of the date and
time that we can use however we need them.
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One of these methods is getHours().
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This will return the current
hour on a 24 hour clock.
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We'll use the getHours() method to
help us figure out what our pet
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is doing right now.
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There's a ton more cool things you can do
with the date object, if you're interested
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go ahead and check out the teacher's
notes for links to more documentation.
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Do you remember how to access
an object's methods using dot notation?
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If you wanna give yourself a quick
challenge, pause this video for
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a moment and try to create a variable
that will hold the current hour
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using the date object and
the getHours() method.
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Otherwise keep following along and
I'll walk you through this step.
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Okay.
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Create a variable called hour using
the const keyword and set it equal
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to today.getHours().
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Great job.
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That was pretty simple right?
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Now we're gonna write the if statement.
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All my pets do is sleep and play, so
my if statement will be pretty simple.
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If the hour is after 8 and
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on or before hour 20,
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they are playing and
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if it's any other hour,
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they're sleeping.
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Feel free to expand on
this in your own code.
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Maybe your pets have a schedule that
include things like going outside,
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having meals or
socializing with other pets.
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When you create an object,
it's entirely your design.
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So have fun with it. Great work.
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You just wrote your first Getter method.
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This special method
allowed you to create and
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dynamically retrieve the value
of a property called activity.
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Even though this property
wasn't declared and
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set in a constructor method
like the other properties were,
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you can access its value the same way,
using dot or bracket notation.
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But remember if you were to output
the ernie object to the console,
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you would not see the new
activity property.
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A value for the activity property is
computed and returned from the getter
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method when we access it, but
never actually attached to the object.
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Let's test this out,
move down toward the bottom of your file,
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after the class declaration.
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On a new line, log the value for
the activity property for
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the ernie object to the console.
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Now let's save the file and run it.
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Try this again now, but
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log the ernie object as a whole.
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Notice how the ernie object doesn't
show an activity property, but
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when we access that property
directly a value is returned.
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Okay, let's take a break here.
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See you in the next video.
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