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Now that we've seen how methods work inside of classes, we're going to take a look at how we handled

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data inside them as well to get started.

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I'm going to clean up this air right here around vehicle honk by deleting that line, and I'll do the

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same thing at the bottom of this file as well.

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All right, it's now back at the top on vehicle, I want to add in to fields, these are essentially

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going to be properties are going to reference actual values.

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Whenever you want to specify a property inside of a class, we'll just write out the name of the property,

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so maybe color and then a type invitation for that property.

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So in our case, maybe a color should be a string like so.

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And right now, as soon as you type out this line of code, you might see an air around this line,

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specifically around color.

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If you don't see an air in your screen, looks like mine, that's totally fine.

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If you do see and there it is, because traditionally we want to initialize a variable any time we declare

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it inside of a class.

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So right now we have declared the existence of a property or a field attached to class vehicle, but

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we have not give it and given it an initial value to do so right after the class or the property definition.

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We can write in an equal sign and then some value.

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In my case I'll say read like so.

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So this means that every time we create an instance of class vehicle, the instance will have a color

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property that is a string and its starting value will be equal to red.

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So, for example, down here, right underneath CONSED vehicle is new vehicle.

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We could do a console log of vehicle, not color like so.

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If we now save this, look back over to our terminal one more time and run that file.

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We'll see a council log of red up here.

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Now, this is just one way to initialize a variable inside of a class.

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It's also very common to want to initialize a variable using some configuration options that we passed

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to the class when we create an instance out of it.

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So, for example, it'd be a lot nicer to specify the color, right, when we create a vehicle, because

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sometimes a vehicle might have a color of red.

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Other times it might be silver or black or orange or whatever it might be.

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So to do so, we could pass in the color as an argument to vehicle right here.

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So maybe I'll do something like orange.

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If we're going to pass in any arguments to this, we have to define a special function inside of the

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class definition called the constructor.

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So I'm going to write out constructor like so the constructor function is a very special function defined

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inside of a class, any time that we define a constructor, it will be instantly executed, right when

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we create a new instance of the class.

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So as soon as we call new vehicle right here, the constructor function is going to run and the arguments

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that function are going to be whatever we pass in when we create the instance.

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So in this case would be a string of orange.

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So we would probably want to receive that as an argument into the constructor of something like maybe

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color with an annotation of string like so.

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And then we'll take that value and do some initial assignment with it inside the constructor, so we

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would say this color is equal to color.

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If we use this method of initializing color by defining the constructor, we do not have to initialize

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it up here.

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So it's usually an either or decision.

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Either you are going to initialize a property on the same line that you define it or you're going to

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initialize it inside the constructor.

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One or the other in this case will stick with the constructor method.

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So I'm going to delete the equals.

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Read up here.

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So now if I save this file again, I can run it in my terminal and I should now see I got a little air

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here.

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Let's see.

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Argument for color was not provided by mistake.

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Let's see.

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Oh, I know what it is.

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We created a car down here as well.

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Let's just comment out all this stuff down here really quickly.

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While we were working on that first class, this actually is a very valuable subject that we have to

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discuss, like what we do with constructor's in extended classes, but let's just hold off on that for

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right now.

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So I just commented out everything in the second half to file.

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I'm going to save the file and then try to run it again.

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And there we go.

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Now I see orange.

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Perfect.

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Now, just you know, there's also a little shortcut to automate this entire process right here to notice

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how we kind of have to refer to these repetitive properties multiple times.

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I see color, color, color all over the place.

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A equivalent way to write all this out by using a little shortcut would be to delete the implementation

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inside the constructor.

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Delete the property definition at the top.

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And then right in front of the color argument, we could add on the word public like so.

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Public is one of those modifiers we spoke about, these modifiers can be used not only on methods in

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a class, but on properties or fields as well.

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So this syntax you see right here is going to mean that we're going to take whatever comes in as the

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first argument to that constructor, which is in this case, it's orange and it will be assigned, as

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an instance, variable of color to our vehicle that we are creating.

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So the code that you see right here is 100 percent equivalent to this right here.

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It's just slightly shortened up.

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So we don't have to refer to the same color, color, color all over the place.

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So we're going to use this shortcut many times in the code that we write, if we do something like this,

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we can then shorten up that body of the constructor function as well.

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Even though it's empty, we still have to put it in.

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So let's try saving this flip back over, run the file again, and we will see orange again.

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All right, now, those modifiers we spoke about apply to variables just the same way as they do to

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methods so we could alternatively use the private keyword or the private modifier on color.

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If we do so, we will no longer be able to read that variable outside of our class anymore.

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Likewise, we could also mark this thing as being protected.

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We still cannot access it outside the class, but we would be able to access that field from a class

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that extends vehicle such as car down here.

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All right, I'm going to leave that variable as public like so and I'll say the file, we're going to

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leave it like this.

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Let's take a quick pause right here.

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We're going to come back the next video and talk about how these fields work when we are using extensions

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like we are down here.

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So quick pause and I'll see you in just a minute.