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In the last two videos, we spoke about some basic topics around in classes that for the most part are

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probably going to be at least a little bit familiar if you have covered 2015 before.

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So now we're going to start to discuss some of the differences between 2015 classes and classes in TypeScript.

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So the first thing we're going to cover is the existence of something called modifiers.

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Modifiers are keywords that we can place on different methods and properties inside of a class, the

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different options are public, private and protected.

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The goal of these different modifiers is to restrict access to different functions or different variables

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by default.

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Every different method and property that we add to a class is always going to have the public, simply

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the public modifier on it.

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Now, the reason I say by default is that right now you'll notice we don't have anything that looks

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like public, private or protected inside of our class.

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So because we did not add anything or any of those modifiers inside of here, it is assumed that these

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are all currently public.

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So what does it mean to actually be public?

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Well, it means that a given method or property, because we can add a modifier on a property as well,

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but we'll discuss that in a little bit.

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It means that method can be called anywhere, any time.

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It's easiest to understand what public means if we then look first at private and protected, if a method

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is marked as private, it means that that method can only be called by other methods in the exact same

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class definition.

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If a method is marked as protected, it means it can be called by other methods in that class and by

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other methods in child classes as well.

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By far, the easiest way to understand all this is to just write out code samples, so let's do that

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right now.

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So right now, back inside of my editor, I'm going to add on the public modifier to all three of these

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different methods, you see, I'm going to say public, public.

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By doing so, I have changed absolutely nothing inside of my code, again, by default, all these different

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modifiers are considered to be public.

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So in general, it's only when we start to add on different modifiers like protected or private, that

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we're going to see any difference.

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Let's try marking the drive method right here as private to get started.

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So I'm going to add on the private modifier to that.

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As soon as I do so, you're going to see an air appear on car drive, it says property drive is private

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and only accessible within class car.

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So that means that we can never call this method from outside of this class.

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Only methods inside this class can actually call drive.

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So let's say, for example, that we had a new method to this thing called start driving process.

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And I'm going to have that with a return type, avoid this method right here, because it is inside

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of a car, can safely call the drive method by referring to this drive like so.

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So now down here on Khadar Drive, rather than calling car drive, we could instead call start driving

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process.

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We can safely call start driving process because it does not have the private modifier on it.

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And start driving process can safely call, drive, even though drive is marked as private because is

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an inside of the same class.

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You'll notice we've got a little air right here if you hover over it.

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We're seeing this air because we have added in a new property or we've modified a property in class

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car that is also existing inside a vehicle as well.

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But in vehicle, our definition up here drive is marked as public.

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So the air here is that we've got a child class that has a different modifier than the parent class.

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If we ever are overriding a method, as we are right here, we cannot change the modifier in the child

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class.

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So in this example, if we remove private life so that air will go away.

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However, if vehicle did not have that method at all, we are no longer overriding it inside of car.

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And so now we can successfully add on private like so.

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OK, so, again, we're going to use private whenever we want to restrict access to a function.

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Now, here's the really important thing, like why do we care about this?

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Right.

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That's the real important definition.

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The first thing I want to tell you and make extremely clear is that we do not mark Method's as being

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private over any type of security concern around like being hacked or something like that or having

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some malicious user.

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We need to find a method as being private, we are not adding in any layer of application security.

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The only reason to mark something as private is to restrict the different methods that other developers

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can call.

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And the reason we want to do that is if we might have a method that very deeply manipulates a class

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and maybe there's some, like, really complicated special way to use it.

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And maybe you and I don't trust other developers to call that method safely.

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If other developers call a given method, they might just inadvertently break something inside of application.

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And so if that's the case, if we have some method that we just don't want other developers to call

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because it's very likely they're going to break something, we will mark it as being private.

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OK, now we've taken a look at private, let's also discuss what protected does, so protecting is just

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like private.

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The only difference is that with protected, we can access the given method in child classes as well.

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So, for example, let's go back up to vehicle right here, rather than saying that Honk is going to

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be public, let's make it as private really quickly.

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And then let's say that when we start the driving process, we're not only going to do a drive, but

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we'll also do a honk.

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So when we try to call Huncke, our class is going to automatically try to call this method, but because

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this thing is marked as private and is in a parent class, we are not allowed to do so.

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So is only accessible within vehicle.

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If we still actually really wanted to call honk, even though it's inside of a parent class, we could

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mark it as protected.

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So now that child class can access that method, but it cannot be accessed by anywhere outside of that

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child class.

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So, for example, if we now made an instance of vehicle right here, so consed vehicle.

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His new vehicle.

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We would not be allowed to call huncke.

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If I try to do so well, very quickly, I see an error message once again.

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OK, so that's the basics of modifiers, so we've now taken a look at basics of classes, methods,

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a very tiny bit around inheritance and modifiers as well.

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So quick pause right here.

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We're going to start to cover fields in the next section.

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So I'll see you in just a minute.