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I'm inside of our publisher t s file inside of here.

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We are creating some piece of data and then publishing it off to the Internet server.

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Now when we take a look at this published code it definitely works right now.

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But I want you to really imagine all the locations where we could very easily make a typo and not really

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have anything to catch that typo.

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If I take a look at this data object I could very easily accidentally define price as a string like

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Dollar Sign 20 instead of Title I could very accidentally put in name on the subject of ticket created

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right here.

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I could very accidentally put in ticket created which is a different channel.

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As far as Napster misery is concerned.

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So even though this code is very simple right now and easy to understand there's an incredible number

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of locations where we could very easily make a typo that would be rather hard to catch when we start

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to deploy a service so in this video we're gonna start to put together a publisher bass class very similar

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to the base listener class we already put together the entire goal of all this is to get typescript

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to check our code and make sure that whenever we tried to emit some kind of event or some data it has

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the correct structure the correct properties the correct types and make sure that whenever we actually

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publish that data we provide a valid subject name inside of here as well.

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That is the goal of all the stuff we are trying to get typescript to help us out and make sure we don't

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make these silly typos.

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At this point just as a side comment this all might seem really unnecessary.

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You might be thinking Steven when am I going to make a typo.

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Well remember on a micro services project the kind of underlying assumption here is that you're going

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to be working on a micro services project with a team and so you need something in place to make sure

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that your teammates do not make mistakes just as much as you need to make sure that you are not going

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to make a mistake.

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It is very easy for people in a team to just very slightly mis communicate on whether some property

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name is title or name.

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You never know.

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So long story short we're gonna write out some code that looks very very similar almost identical to

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the base listener class.

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It's gonna be an abstract class.

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We're going to try to have some coupling or checking using a subject and some other kind of argument

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thingamajig or something like that.

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Let's just get to it and start writing some code inside of my events directory.

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I'll make a new file called base publisher dot.

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Yes inside of here I'm going to immediately add in a couple of imports.

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I'm gonna get Stan from node Nat streaming and I'm going to get our big list of subjects from subjects

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and then going to define and export an abstract class called publisher I want us to be a generic class

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because this is how we're going to eventually enforce some type checking on the subject for all the

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different subclasses a publisher we put together.

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So this is going to be a generic class we're going to accept some type that we're going to refer to

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as t and it's going to extend event let's define that event interface right above so in order to be

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an event you must have a subject and a subject must be one of the subjects listed out inside that subjects.

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Enum you must also have a data property and type can be any.

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We don't really want to enforce any specific data type around this based interface now inside a publisher.

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We're going to do something very similar that we did inside of our listener where we're gonna say that

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this thing has a couple of different abstract properties so we're not gonna use this publisher directly

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same way we did not use the listener directly.

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We are going to subclass publisher and have different publishers that are meant to publish different

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kinds of events so we're going to define an abstract property of subject and this must be equal to the

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custom type right here or the generic types subject property our publisher is also going to need a copy

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of the Nats client that hopefully has already been initialized inside our application so we'll make

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sure this thing has a constructor where we're going to receive some client of type Nats.

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I'll make sure that I update the client property and I'll make sure sorry not that Stan is such an easy

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thing to forget who came up with that they should really show is called a client but I digress.

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Also make sure that our class has a property of Klein as well.

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We'll say client will be of type Stan.

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I'm gonna make sure this thing is marked as private just so no one else tries to reach in and mess around

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with it at all OK.

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So now we need a function that is going to actually start to publish some information just as we had

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the listen function inside of our base listener class.

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No listen right here.

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This is what actually reached out with the Stan client and created a subscription.

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We want to have a function very similar to that inside of our publisher.

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And the goal this function is going to be to take some data or like an event data and publish it off

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to the Nat streaming server.

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So we're going to define a function called publish this thing is gonna take some data that we want to

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publish and its type is going to be up type T data

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then inside of here we're going to make use of our Nat's clients very similar to how we did back over

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here inside of our publisher t s file.

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We're going to call publish on that client.

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We're going to provide the subject that we want to provide this or publish this data as a then the data

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as a second argument.

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So inside of here we'll say this stock client publish

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the subject that we want to publish this event too.

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It's going to be the subject property.

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So this subject and the data that we want to be publishing is the data argument data.

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So now there is an optional third argument here of a callback function.

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We're going to come back and work with this callback function in just a little bit.

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But right now whenever it gets executed after we publish this event let's just do a console log of event

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published.

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And like I said it will eventually come back and do something a little bit more with the callback.

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All right.

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So believe it or not that is pretty much it for this abstract publisher base class.

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It's now just the same as what we're doing with our listener.

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This is the definition of what a publisher is.

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We're now going to subclass the publisher into something that can actually publish very specific kinds

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of events such as a ticket created event so inside of my events directory I'm going to make a new file

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called Ticket created publisher T.S. inside of here at the very top we will import the publisher that

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we just created from base publisher I will also import yet ticket created events from ticket created

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events.

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And then finally I'm going to get our subjects into

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from subjects that inside of your we're going to export a class called Ticket created publisher and

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it's going to extend publisher and because we are making use a publisher remember a publisher is a generic

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class which means we have to provide a type arguments.

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So the type of event that we're trying to publish here is a ticket created event.

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So we'll stick and ticket redid events like so

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then we're going to define the subject.

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If we hover over this as a matter of fact it'll tell us we have to define the subject very similar to

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what we did inside the listener.

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We're going to say the subject must always be of type subjects dot ticket created and the actual value

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from it must be subjects to get created and that's pretty much it.

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We do not have to define a publish function here we already define the Polish function inside the publisher

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based class.

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So how would we actually make use of this.

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Well this video is running a bit long.

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Let's take a quick pause right here.

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We'll come back the next video and then see how we actually make use of this custom.

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Publisher.