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In this video we're going to start implementing class listener inside of our little test project now

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between the last video on this one.

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I want you to notice I added on another abstract property here of Q group name.

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So that means that we're going to have to define an actual value for Q Group Name inside of our subclasses

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of listener okay.

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So let's go back over to our Ed inside of our listener test file.

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We're going to define this listener class at the very bottom will eventually move this to its own separate

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file but right now this will work just fine down here.

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We're going to create an abstract class called listener.

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We're going to go through all the properties and add them in one by one along with some implementation

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for each.

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Let's first take care of this client thing.

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So we want our class listener to have a client property that should be a reference to a pre initialized

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Nats client.

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So it should be a type stand.

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When I say pre initialized I mean to say that we should have already connected to Nats successfully

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to the client we're going to pass in is essentially and be like that thing right there.

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After we have successfully connected

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so I'm going to assume that this thing is going to have a private property client and it is going to

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be a type stand a stand right here.

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As you'll recall is Nats backwards.

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This is what the Nats community calls clients.

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We need to import this Stan type from the node Nats library at the very top of the file so I'll find

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no not streaming and I'm going to get the Stan type and then back here.

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We now have an around client is just saying that we have defined as property but we never initialized

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it.

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Let's make sure that we defined a constructor function and we're going to make sure that the constructor

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receives a client that we're going to use.

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It's all defined the constructor will say this thing is going to receive a client property that is of

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type stand and we're gonna take that and assign it to clients.

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So this client is client.

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Next up we're going to make sure that we define a Q Group name and a subject.

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These are both going to be abstract properties which means they must be defined by our subclass.

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So I will put in at the very top of the class abstract subject like so that's going to have type string

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and abstract you group name that will be a string as well.

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Those are easy let's now take care of equate.

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So this will be the number of seconds we have to listen to a message and act it before the event.

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Eventually times out so I'm going to define this as private equate and let's actually make it protected

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instead which means that the subclass can define it if it wants to go into default is to be five seconds

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so five thousand milliseconds five seconds.

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Next up subscription options are subscription options and total are gonna be very similar to the options

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we had written out up here.

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We're just to find them inside of a helper method.

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Just have one convenient location for them.

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So define subscription options inside of here we go.

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We will return this stock client no client is our Nats library or Nats instance not subscription options

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you're gonna chain on a couple of different options to this thing versus say set deliver all available

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remember that's gonna make sure that the very first time our subscription is created we get all messages

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on this channel that have ever been emitted well then set manual act mode to true.

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We're gonna set that equate to this not equate.

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So that's how we customize the acknowledgement time out period normally 30 seconds.

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But again we're going to certain that down to five seconds and then finally we'll also set up our durable

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name set durable name for the durable name.

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We're just going to end up using the same Q Group Name so we're going to use the Q Group Name both as

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the Q Group Name and as the Journal name because it usually makes a lot of sense to just use the same

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one.

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It's very rare that we're going to distinctly want these things to be different.

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So for set terrible name we will pass in this dot Q Group Name

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after that.

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Let's put together our listen method to the goal of listen is to really just set up the subscription

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itself.

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Whenever we get an incoming message we're going to pass the message using a pass message method and

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then eventually call an on message method so inside of a listen right here we're going to first create

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the subscription itself so cons subscription is this client subscribe and we're gonna pass in those

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three arguments the first one is going to be the subject that we want to listen to.

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So this not subject

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the second is going to be our Q Group name

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and then third will be our actual subscription options.

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So we'll call this dot subscription options

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that will give us our subscription after we get it.

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We have to start to listen to it.

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We'll stay on message.

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We're going to receive MSP which is of type message inside.

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We'll do just a little bit of logging info just to say hey we just received a message so that we can

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more easily see when we receive messages and they're being dealt with inside of our app.

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So do a console log I'm gonna put a little new line inside of here because the log that we're gonna

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do is a little bit long.

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I'm gonna put in a template string so back ticks and we'll say Message received we're going to print

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out the subject of the message that we just got and maybe we should also print out the Q Group name

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for this thing as well just we understand exactly what group of services receive this message.

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So I will also print out this dot Q Group Name

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after that.

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We're going to want to pass the incoming message and pull the data out of it.

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So I'm going to really quickly define R's message down here.

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So remember when we get a message we have to call that get data method on it.

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That's gonna give us either a buffer or a string.

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We're going to make sure that if it is a string we just person data out of it and return the results

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of that so we're going to assume that we're going to receive a message in this thing of message.

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We'll get our data out.

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So message data

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then if we are working with the string or a buffer remember it can be either we mouse over data right

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here we'll handle it appropriately we're gonna use an attorney or expression to do this.

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So we'll say return type of data equal to string.

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So if it is a string I want to do either one thing or the other.

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So just a normal ternary expression.

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So if it is a string let's go ahead and do a J signed up pass of data otherwise if it is a buffer we'll

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handle it appropriately.

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Here's how we would handle a buffer.

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We don't ever expect to get a buffer but we're gonna write some code to handle it just in case we'll

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do a Jason pass data dot to string UTF 8.

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That's how we would pass a buffer and get some Jason out of it.

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So back inside of this subscription dot on we will call or get past data and that's going to come from

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this dot pass message and we'll pass on the message or excuse me MSE and then finally we are going to

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assume that there is some kind of on message event or me on message method that we want to call with

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this event data that we just passed out of it.

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So I'm going to try to call this dot on message with the pass data and just for consistency sake we

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don't really know what we want to do inside of.

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On message just yet.

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So in addition to the actual data that we're gonna throw in there let's just pass in the entire message

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the original one as well just in case we need to get access to some other property off the message itself.

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So it's and message like so we are getting an air out of on message.

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So we do have to define that as an abstract method on our class.

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And again by being an abstract method that means we must define it inside of a child or subclass.

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Well very quickly define on message at the very top by all of our other properties about by all the

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other abstract ones.

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So we'll say abstract on message and we're going to assume that this is going to take in some data right

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now we'll say that it's of type any and a message of type message and it's going to return void okay.

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So that is our class listener lot of code inside of here.

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But really all we did was kind of massage a lot of the stuff that we already wrote out.

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This is all the same stuff we already put together up here.

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We just kind of redistribute it around.

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Let's take a pause right here.

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When we come back next video we're going to take a look at how we can now subclass this thing and very

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easily create a listener.