110. Injecting the Logging Service into Components

Jul 15, 2026 04:40 · 6:21 · English · Whisper Turbo · 2 वक्ता

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S… Speaker 1 (110. Injecting the Logging Service into Components)

In the last lecture we created our service and I told you to not instantiate

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it on your own.

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I told you that Angular offers some great tool which will give us

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access to our services.

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It's Angular's dependency injector.

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What is a dependency injector?

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Well, a dependency is something a class of ours will depend on.

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For example,

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the new account component depends on that logging service because we

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want to call a method in that service.

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And the

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Dependency Injector simply injects this dependency,

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injects an instance of this class into our component

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automatically.

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All we need to do is we need to inform Angular that we require

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such an instance.

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So how do we inform Angular that we require such an instance?

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We add a constructor to the class,

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to the component,

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in this case where we want to use our service.

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So there I can bind it to a property by using

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this TypeScript shortcut of adding an accessor in front of the name of the argument

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to instantly create a property with the same name and bind the value to

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it. So here I will name this logging service.

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This name is totally up to you.

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Now this is the important part here though.

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Add a type assignment here.

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This is not optional.

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You need to set the type and the type has to be the class you want

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to get injected.

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Logging service in this case.

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Make sure to also add the import at the top.

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Now, let me close the body of this constructor.

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And this simple task here informs Angular that we will

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need an instance of this logging service.

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Correctly,

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you might ask,

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well, how do we inform Angular?

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Why does this matter if we write this in the constructor?

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Think about who gives us the instance

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of this account component,

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this new account component here.

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This is a TypeScript class in the end,

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so somewhere this needs to get instantiated so that something happens in

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our app.

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Well, who is responsible for creating our components?

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Angular is,

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of course, because we're placing selectors in our templates.

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And when Angular comes across these selectors,

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it gives us instances of our components.

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Now,

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since Angular is responsible for instantiating our components,

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Angular will need to construct them correctly.

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So if we define in the constructor that we require some

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argument, Angular will recognize this.

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And now it tries to give us that argument.

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It tries to give us this,

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well,

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type in this case.

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So it knows we want an instance of the logging service

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class because we define the type here.

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This is why this is important.

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Now that is almost enough,

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but not quite.

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Now Angular knows what we want,

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but it doesn't know how to give us such an instance.

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We need to do one additional step.

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We need to provide a service.

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Provide simply means we tell Angular how

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to create it.

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And that sounds very complicated and it is very simple.

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All we have to do is add one extra property to the addComponentDecorator,

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the providers property here.

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This also takes an array like other properties we added before.

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And here we again just have to specify the type

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of what we want to be able to get provided,

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you could say.

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So logging service again.

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Now with that,

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Angular, when analyzing the component,

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recognizes that it should be able to give us such a logging

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service and it will set itself up to be able to do so.

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And when it then actually...

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builds the component,

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constructs it,

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it sees that we want to have such an instance,

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and it will know how to give us such an instance.

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And now,

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we can simply,

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in our component,

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anywhere in this component,

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access our LoggingService property,

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which is created automatically since I used this TypeScript shortcut here,

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and call LogStatusChange.

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So now I'm not creating that instance manually,

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Angular does it for us.

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And why is this better than creating it manually?

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You will see some other advantages later,

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but this basically lets you stay in the Angular ecosystem.

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And Angular knows how your app works.

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Again,

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some other advantages will come up later.

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So with this,

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we now have the same code as before.

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So if we have a look at our application again and create

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a new account,

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we still see the log here.

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depending on which status we chose here.

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So this still works,

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but now we're injecting the service.

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Now let's also do the same by copying that

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in the account component here.

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So here I will also add the constructor.

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And of course here we also need to add the import because

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TypeScript needs to know where this logging service comes from.

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Not Angular,

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TypeScript.

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And I will also add my provider,

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of course, because for this component too,

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I need to inform Angular how to create this logging service.

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So if we do this and then go

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back to the application here,

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let it reload,

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create a new service again.

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This works.

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Now let's change the status and this also still works.

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Now,

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of course, because I didn't replace this here,

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so let's call the logging service now and

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call log status change and pass the

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status.

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Now,

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if we save this,

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and try to change this,

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it still works.

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So now we got this same logging functionality outsourced

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centralized in a service.

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And therefore our code here is a bit leaner.

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And I guess you can imagine how in bigger applications where you have

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duplicate code,

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a service can really help you to get more dry to don't

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repeat yourself all the time,

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but instead to really cleverly outsource your code

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into a service and have it there.

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