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Advanced NestJS techniquesPart 4Logging Redis commands, Create a Chrome extension with OAuth, AWS, React, Typescript, and Webpack, These 4 Websites Will Improve Your Web Development Efficiency, Small JavaScript Tricks That Save Your Time, Parse Firebase Timestamp using rxjs pipe with moment. To have tree-shakable services? If you want additional bootstrap initialization logic, then APP_BOOTSTRAP_LISTENER is designed for that. -
E.g. Heres a short guide how to do all that at the same time. Makes sense, using any will help OP achieve what he wants to. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. This part is pretty much the same as in the angular guide. see these two github threads: The providedIn syntax seems to have 2 main benefits: But you only really need (1) if you're writing a library rather than an application (because why would you include a service that you didn't need in your application), and you can avoid multiple service instances (2) just by making sure you don't import the service module more than once. By clicking Sign up for GitHub, you agree to our terms of service and -
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[UPDATE]: I found a blog describing in more details the navigation example: https://blog.hackages.io/our-solution-to-get-a-previous-route-with-angular-5-601c16621cf0. @mlc-mlapis That is a valid reason; it should still be explicitly pointed out in the documentation. Because if you simply put constructor(private service: Service) {} into the root module and never use this.service, the code in the service is still executed. We need an app module with the root routes. and i have want to use the providedIn syntax in order to mark the scope of the resolver service. This isn't an Angular dependencies problem. For basics we lazy load modules which are not needed immediately, have a special purpose or contain a well defined separate feature. https://blog.hackages.io/our-solution-to-get-a-previous-route-with-angular-5-601c16621cf0, Angular LanguageHelper service not created anymore. So if you had any doubt, then I vote for adding it into the docs. For more interesting stuff, feel free to follow me here or on LinkedIn. Registering the provider in the @Injectable metadata also allows Angular to optimize an app by removing the service if it turns out not to be used after all. Refer: angular.io/guide/providers#provider-scope - Krishna Mohan. @julianobrasil If it's not injected, then likely no one has reference to that class, and it will be dropped away by tree-shaking without any trace at runtime. I am wondering how the new angular service decorator. Ozgur, I have to "inject" (register is more correct) the resolver in the routes for the resolve phase. Also, I suggest adding a property for the @Injectable annotation to toggle this feature. Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque
If some final decision is made as to whether or not the docs should be updated, I'd be happy to work on a PR :).
It boils down to services being easier to tree shake when they are provided by the root module, as I gather. @trotyl , @matsko , @dariobraun , @mlc-mlapis , @ericmartinezr : If one of you can concur, I'll move forward with this issue to make the change. In our example, we dont need the loader service to download hls.js on the server.
Now this approach alone doesn't work of course since the service is not injected anywhere, but is supposed to just live as a singleton instance, instantiated at app start. In this case, providedIn: 'root' specifies that Angular should provide the service in the root injector. So far it hasn't caused me any problems, but the caveats below still remain and I believe it's important to remain aware of this.
but the line
It boils down to services being easier to tree shake when they are provided by the root module, as I gather. @trotyl , @matsko , @dariobraun , @mlc-mlapis , @ericmartinezr : If one of you can concur, I'll move forward with this issue to make the change. In our example, we dont need the loader service to download hls.js on the server.
Now this approach alone doesn't work of course since the service is not injected anywhere, but is supposed to just live as a singleton instance, instantiated at app start. In this case, providedIn: 'root' specifies that Angular should provide the service in the root injector. So far it hasn't caused me any problems, but the caveats below still remain and I believe it's important to remain aware of this.
but the line
doesn't react evenwhen I forced to add privacy statement. -
In those cases you can shave off as much as a few seconds by this lazy loading from your load time (Time to Interactive) on slower networks, and lets face it, not everybody has access to a 5G network speeds and latest iPhones. We provide this VideoService through a module provider, and that is where well check the condition and ask for the singleton of the HlsLoaderService or an empty NoopService alternatively. Something like "Note that an instance of the Service is only created if there is at least one class asking to inject it.". Simply check your browser console and comment in/out the constructor in the app.module.ts file. Turns out the solution is "don't do it", as explained in this thread by one of the Angular guys: https://github.com/angular/angular-cli/issues/10170#issuecomment-380673276. i'm silly :). Sign in RJM, use providedIn: any, after Angular 9, checkout my answer -
(Saves unnecessary reading and confusion) -
To summarize: The section of the doc to be fixed is Provide the HeroService in the Tour of Heroes Pt. it's not the case that you haven't injected it anywhere. in Angular 9+ you can use providerIn: any, checkout my answer - maxisam, I ran into the same problem. minigeek. With careful planning, lazy loading can solve all these issues and more. It's a robust alternative to 'root' to make sure the individual modules don't have a side effect on each other. MessageService doesn't work like totally unassigned instance. And that's what I would do if eager: true: create an instance of the service. ZDiTect.com All Rights Reserved. If it is never used it will not be contained in the build (tree shaked). RtmY, Instead of injecting your service in Routes, use constructor. I want to mark this answer but i hope somebody will give a solution for this problem. Very similarly to lazy modules, lazy third-parties work by utilizing ES6 module `import` function. Thanks for that..check my new commenf -
This is the class well use in our components, effects, other services, this is going to be our public API so to speak. Meaning if I have a lazy loaded module, with a service that is providedIn root, will this include the specific service in the applications base code, aka. If you provide a service by setting {providedIn: 'root'} the service should be created according to the docs. There might be use cases where you just need to add independent pluggable functionality that will not be used in any component or directive or service but you want a class which can use other services by injecting them and and do some calculations. Avius. This approach both endorses single-responsibility-principle and solves the issue of polluting AppComponent with all sorts of event listeners. RtmY, It's a bad answer anyway :-) -
@ericmartinezr The documentation is still not correct: The service instance is not created if it isn't asked for (the first part of the sentence is completely independent from the second). The service instance is not created if it isn't asked for (the first part of the sentence is completely independent from the second). You should always provide your service in the root injector unless there is a case where you want the service to be available only if the consumer imports a particular @NgModule. In other words, it is in a different injection tree. There are cases though, when we know beforehand, that certain features (their implementing services) wont be utilized, and it is not dynamic in the lifecycle of that module, e.g. Creating Android/iOS App with Cordova and Angular, Angular Best Practices: Accelerate Your Angular App, https://github.com/amdor/conditional-provider, We want to lazy load the video player pages route, since it is going to be an independent unit inside the application, We use a third-party lib hls.js for streaming and we want it to load just before being used, not a minute earlier, We want our services to be tree shakeable (even if they wont be shaken in this example), We use some sort of configuration to enable/disable the loading of HLS, but also the initialization of its loader service. When you provide the service at the root level, Angular creates a single, shared instance of HeroService and injects into any class that asks for it. As of angular 10, you can also declare providers in components that are scoped only to that component's hierarchy. Currently, when a service is registered it will end up in the final bundle even if it is not used. https://stackblitz.com/edit/angular-nsy3vj?file=src%2Fapp%2Fapp.component.ts. takanuva15, Use providedIn: any, after Angular 9 -
This is a translations resolver which I use in a protected module: I declared the translations resolver service in the protected routing module: Because of the fact that I import (typescript import) the protected.module in the translations-resolver.service.ts in order to use it in the providedIn attribute I get a WARNING in Circular dependency detected: The 2nd path (protected/protected.module.ts) is added due to the providedIn attribute. But most answers are talking about what's not OPs requirement but an alternative. Today, we are a multi-national company employing some 1,900 people from 55+ nationalities in 11 locations across the world. For a good reason too. Add a disclaimer to the docs? - S.D. Then we need a feature module with the child routes, which will be loaded only when the user navigates to `/video`, through `import(./video/video.module).then(m => m.VideoModule)`. When using providedIn: 'root' the Angular compiler will figure out the perfect way automatically: For further informations consider reading the documentation and NgModule FAQs, Angular the purpose of providedIn with the Injectable decorator when generating Services in Angular 6. why am i getting so many friend requests on facebook 2020, How to pass dynamic value in href in javascript, Magento 2 proceed to checkout not working, change bar chart color based on value python. works in conjuction with lazy loading. I didn't get the first solution can you show some code please. Ozgur i'm not sure how this can help in my case to solve the circular dependency. @dariobraun It's already documented, but there could be some docs change to make it more clear. I've followed the tutorial at https://angular.io/tutorial/toh-pt4 up, but it's not work properly. Have a question about this project? MessagesComponent, HeroService have a correct constructor for injectable service of MessageService. Thanks. So that isn't zero reasons - and is in fact my exact scenario. Provider scope link When you add a service provider to the root application injector, its available throughout the app. Murhaf Sousli, Angular 9 has another solution, any. -
But IDEs mark service as unused. If you add the eager property, what will you do with the service if it hasn't been injected anywhere? more, It supports tree-shaking of unused services, The circular reference problem described above. rem aperiam. oh, I found it. maxisam, Basically it works just like module, but you don't use module directly so no more circular dependency, Doc: https://angular.io/api/core/Injectable#options. If you liked this short article, dont forget to destroy the clap button. Step forward the providedIn attribute a new way to declare a tree-shakable provider. maxisam. What would be the preferred way to handle this? angular.io/guide/providers#provider-scope, angular providedin cannot access before initialization, https://github.com/angular/angular-cli/issues/10170#issuecomment-380673276, https://github.com/angular/angular-cli/issues/10170, https://github.com/angular/angular/issues/25784, https://angular.io/api/core/Injectable#options, Learn
[Edit] I adjusted the OP (removed "Bug Report" since the behavior is obviously intended) and simplified the stackblitz code example. It has always been like that.
Lazy loading is all the rage nowadays, especially in Angular. The service will be available application wide as a singleton with no need to add it to a module's providers array (like Angular <= 5). @HeeCheol-Kim and what is the Length in
Lazy loading is all the rage nowadays, especially in Angular. The service will be available application wide as a singleton with no need to add it to a module's providers array (like Angular <= 5). @HeeCheol-Kim and what is the Length in
? Thanks to the factory capability of module provider we can define any custom logic we see fit for the actual provide. I faced this many time specially in resolver. Since our code is well organized, based on clean code, separation of concerns, single responsibility, etc., chances are well have a loader service for third-parties like the video loader. @ericmartinezr, it's not the case that you haven't injected it anywhere.
: You should put the addendum at the top of your answer as something like Update Oct 2019 so people read it first before your old answer. 'any' : Provides a unique instance in each lazy loaded module while all eagerly loaded modules share one instance. I just found myself cleaning up the root level app.component.ts which is the place where devs (including me) put all the global event handling logic such as subscribing to the Angular router events. @dariobraun yep. - Check forwardRef() function from angular/core. Each time i try to use a specific service in a module scope (and not root) in throw some circular dependencies warnings. If you provide a service by setting @Injectable({providedIn: 'root'}) the service is not created if it is never asked to be injected. That's why I suggested adding a flag to instantiate it anyway; something like: I'm pretty sure this has been the behavior since like forever. The problems with the providedIn syntax are: This is contrary to official Angular guidance, but my advice would be: Don't use providedIn, unless you are writing a third party library which requires tree-shaking - use the old (not deprecated) providers syntax on the module instead, i.e. If the service is only used within a lazy loaded module it will be lazy loaded with that module. maxisam, @maxisam any is not meant for that. To me it seems like this issue would not occur in any 'real' use cases and further clarification in the docs might not be necessary/useful. But how strange it would be injecting routingStateService: RoutingStateService in the AppComponent and not using it anywhere (maybe tslint would complain about the not used variable). As long as there is an import statement, the problem will remain unsolved. minigeek, @maxisam your answer helped me understand any better lol. How to use ESLint on your Angular Project using VSCode. You signed in with another tab or window. bharath muppa, The second solution makes it un-treeshakable - It makes the service available when its module has been loaded lazily, but does not instantiate the service unless the conditional provider provides it. 'Any' is very helpful to make sure a service is a singleton within module boundaries. From Angular doc: When you provide the service at the root level, Angular creates a single, shared instance of HeroService and injects into any class that asks for it. Now you can import that module into ProtectedModule and you won't get a circular dependency error when loading ProtectedRoutingModule. I can fix this by just providing the translationsResolver as a NgModule provider (in the providers array) but I prefer it to be an injectable provider. Remember that JS is case sensitive. For the full working example see https://github.com/amdor/conditional-provider. @dariobraun but this is the basic assumption and the main reason why tree-shaking exits. The difference is that today the service is not part of your final bundle (tree-shaking), but services don't work by themselves, they need to be injected somewhere. Its a bigger issue than ever to keep our initial bundle size low. If you want to limit the scope so no other developer will ever use your service outside of a particular module, use the provider's array of NgModule instead. Lazy loading third-parties makes sense when their use is local, tied to a specific feature, and when they are not needed for the first render. It allows to refer to references which are not yet defined.
Use the providers array of ProtectedModule. it means a member veriable(string array)'s count of MessageService class. In that article the author suggests doing something like (in you AppComponent): Here we see the calling to the service loadRouting() method could be avoided by putting it's logic inside the service's constructor. Other types of providers can create their values lazily; that is, when they're needed for injection. You could build a service with some code like this: But if you don't inject the service in the app.module.ts, for example, it will not be instantiated until it's injected in some component that needs it too late for it to be useful to that component. The text was updated successfully, but these errors were encountered: @pfeileon isn't it the reason why this new syntax was introduced? 4. I don't know if there are many other use-cases for eager instantiation but if the service only subscribes to events and is never injected, this feature would come in handy. And you just want to know about this navigation information, for example, in components where you have "BACK" buttons available to the user (not the browser ones, but your app provided buttons). To make things generic we create a VideoService thats an Injectable abstract class with all of HlsLoaderServices functions as abstract functions (the blueprint). If this issue is actually the expected behavior, (edit: it is) the docs should explicitly point out that the service is only instantiated if injected at least once. We use tree shakeable services in our libraries, so the bundle size is as small as possible when the application is loaded. Additionally, these providers are also available to all the classes in the app as long they have the lookup token.
Technically, the task is a bit more interesting: The first three are fairly straight-forward, but the fourth requirement might need some clarification. @mlc-mlapis Yeah, absolutely! to your account. The trick here is that our service (HlsLoaderService) wouldnt be exposed from the library its defined in, or in our case it wont be used directly by any other components/services, only by the module that provides its blueprint conditionally. The circular reference is generated by the TypeScript compiler when it tries to resolve the circular imports. Key fixes are in this comment (proposed disclaimer) and this comment (existing documentation) to help understand the disclaimer. I'm trying to provide a resolve service via the new providedIn attribute.
But how do we initialize a (root level singleton) service on demand, when certain criteria is met, while preserving tree shake-ability? The latter loads a video from assets and plays it, the former is only a landing page. - . If you don't want a application-wide singleton use the provider's array of a component instead. To do that, one way is to start a service that observes the navigation and store the last navigated url or something like that. -
We can send HTTP requests directly from the home component but thats not really the recommended way to do it here comes the role of Angular services. Yes in this case it will be only part of your lazy-loaded module/chunks. While the workaround proposed at Stack Overflow works, I find it sub-optimal compared to the solution presented by OP. Copyright 2010 - https://indepth.dev/posts/1151/a-deep-dive-into-injectable-and-providedin-in-ivy. All we need to do to make our services tree shakeable is to add `providedIn: root`, hence making it root provided/singleton service for the whole application. - All From a single slot machine in 1963 to being listed on Nasdaq Stockholm and holding gaming licenses in 18 jurisdictions, Betsson Group has come a long way. Create a new module named ProtectedResolversModule and use providedIn: ProtectedResolversModule and move the resolvers there. Well occasionally send you account related emails. we use server-side rendering and on the server side we dont want these features initialized, or used. Anyway, the main reason for me opening this issue is the fact that the documentation is misleading and should be more specific. I think Angular have made a bit of a mess of the providedIn syntax. Copyright 2022 IDQNA.COM. It seems to have confused a lot of people. RtmY, This is not good. I am used to repeating some facts because I want to be sure that it's understandable (better twice than once ) and it's my vice. The main issue is that maybe you want it to be started along with the application to grab useful information that you will need in the future when you instantiate some component that injects it. Load times are one of the most basic, most important, oldest KPIs of any webpage, especially for the first load time. It is actually not. If nothing is using such a service then why to have it in the code? A classic example is when you want to keep track of the last route the user visited on the app (or maybe the user navigation history during the last hour). At that moment, if you need your navigation history to go back to the last visited page, you won't have it because the service would have just been started at that time. It is not the same instance you used in other module. Since official (and widely followed) Angular policy is to use providedIn: 'root', I decided that on the whole it would be less confusing for other developers if I just stuck with this. Simon_Weaver, Disappointing indeed, although I have to say this hasn't caused me any issues thus far. They also tend to have all services waiting in the memory while you may not even use them ever. First of all we need a service to provide. "{ providedIn: 'root' }" does not instantiate services as documented. When you provide the service at the root level, Angular creates a single, shared instance of HeroService and injects into any class that asks for it. document.write(d.getFullYear()) DarkNeuron, That referenced comment got very badly voted down - plus the comment says "With tree shakeable providers, you now have zero reasons to provide a service from a module (there is a rare case on some lazy loaded services with a component using the service from a separate lazy module)." Already on GitHub? In the scenario mentioned, this service will be initialized, loaded into the memory and waiting to be called to load the video module. @HeeCheol-Kim really? We want to create an application with 2 screens, a home page and a video player page. - An Angular service is a TypeScript class that encapsulates a set of similar functionalities, like fetching data from a server, in your projects code. As a long-time user of various DI-containers, I also vouch for the idea of adding the eager: true flag for the @Injectable() decorator. Theres a new attribute in Angular 6 and you need to start using it. minigeek, @maxisam yes, you are right :). So being your average object-oriented Joe, I obviously ended up creating RouterEventHandlerService and isolating the event handling logic there. var d = new Date() the capital 'L' was the problem! https://dev.to/christiankohler/improved-dependeny-injection-with-the-new-providedin-scopes-any-and-platform-30bb. Heres where it all fits together. I've received 5 up-votes now for this answer, so I feel as though I ought to come clean and say that I'm no longer actually following my own advice on this (below)! Which one of them should i remove / change according to your solution? Dynamic third party loading solves issues which are dynamic in view of the application/module lifecycle, such as `we wont need the video player while the user is logged out`. the app root chunks.js or will this still lazy load the service and later make it a global singleton, when I lazy load that module. We might even use dynamic import for our ES6 modules (/packages) that we dont need immediately after loading its containing Angular module. Thanks! rights reserved. As is, the "Tour of Heroes"-doc is misleading. some message string elements in MessageService's constructor. Injector takes care of providing the services HlsLoaderService would have as dependency, without which we couldnt even access the root provided singleton, rather wed need to manually create one, while also manually passing through its dependencies. SPAs such as Angular apps tend to load all the routes code, including all third party packages you might only use later.
: You should put the addendum at the top of your answer as something like Update Oct 2019 so people read it first before your old answer. 'any' : Provides a unique instance in each lazy loaded module while all eagerly loaded modules share one instance. I just found myself cleaning up the root level app.component.ts which is the place where devs (including me) put all the global event handling logic such as subscribing to the Angular router events. @dariobraun yep. - Check forwardRef() function from angular/core. Each time i try to use a specific service in a module scope (and not root) in throw some circular dependencies warnings. If you provide a service by setting @Injectable({providedIn: 'root'}) the service is not created if it is never asked to be injected. That's why I suggested adding a flag to instantiate it anyway; something like: I'm pretty sure this has been the behavior since like forever. The problems with the providedIn syntax are: This is contrary to official Angular guidance, but my advice would be: Don't use providedIn, unless you are writing a third party library which requires tree-shaking - use the old (not deprecated) providers syntax on the module instead, i.e. If the service is only used within a lazy loaded module it will be lazy loaded with that module. maxisam, @maxisam any is not meant for that. To me it seems like this issue would not occur in any 'real' use cases and further clarification in the docs might not be necessary/useful. But how strange it would be injecting routingStateService: RoutingStateService in the AppComponent and not using it anywhere (maybe tslint would complain about the not used variable). As long as there is an import statement, the problem will remain unsolved. minigeek, @maxisam your answer helped me understand any better lol. How to use ESLint on your Angular Project using VSCode. You signed in with another tab or window. bharath muppa, The second solution makes it un-treeshakable - It makes the service available when its module has been loaded lazily, but does not instantiate the service unless the conditional provider provides it. 'Any' is very helpful to make sure a service is a singleton within module boundaries. From Angular doc: When you provide the service at the root level, Angular creates a single, shared instance of HeroService and injects into any class that asks for it. Now you can import that module into ProtectedModule and you won't get a circular dependency error when loading ProtectedRoutingModule. I can fix this by just providing the translationsResolver as a NgModule provider (in the providers array) but I prefer it to be an injectable provider. Remember that JS is case sensitive. For the full working example see https://github.com/amdor/conditional-provider. @dariobraun but this is the basic assumption and the main reason why tree-shaking exits. The difference is that today the service is not part of your final bundle (tree-shaking), but services don't work by themselves, they need to be injected somewhere. Its a bigger issue than ever to keep our initial bundle size low. If you want to limit the scope so no other developer will ever use your service outside of a particular module, use the provider's array of NgModule instead. Lazy loading third-parties makes sense when their use is local, tied to a specific feature, and when they are not needed for the first render. It allows to refer to references which are not yet defined.
Use the providers array of ProtectedModule. it means a member veriable(string array)'s count of MessageService class. In that article the author suggests doing something like (in you AppComponent): Here we see the calling to the service loadRouting() method could be avoided by putting it's logic inside the service's constructor. Other types of providers can create their values lazily; that is, when they're needed for injection. You could build a service with some code like this: But if you don't inject the service in the app.module.ts, for example, it will not be instantiated until it's injected in some component that needs it too late for it to be useful to that component. The text was updated successfully, but these errors were encountered: @pfeileon isn't it the reason why this new syntax was introduced? 4. I don't know if there are many other use-cases for eager instantiation but if the service only subscribes to events and is never injected, this feature would come in handy. And you just want to know about this navigation information, for example, in components where you have "BACK" buttons available to the user (not the browser ones, but your app provided buttons). To make things generic we create a VideoService thats an Injectable abstract class with all of HlsLoaderServices functions as abstract functions (the blueprint). If this issue is actually the expected behavior, (edit: it is) the docs should explicitly point out that the service is only instantiated if injected at least once. We use tree shakeable services in our libraries, so the bundle size is as small as possible when the application is loaded. Additionally, these providers are also available to all the classes in the app as long they have the lookup token.
Technically, the task is a bit more interesting: The first three are fairly straight-forward, but the fourth requirement might need some clarification. @mlc-mlapis Yeah, absolutely! to your account. The trick here is that our service (HlsLoaderService) wouldnt be exposed from the library its defined in, or in our case it wont be used directly by any other components/services, only by the module that provides its blueprint conditionally. The circular reference is generated by the TypeScript compiler when it tries to resolve the circular imports. Key fixes are in this comment (proposed disclaimer) and this comment (existing documentation) to help understand the disclaimer. I'm trying to provide a resolve service via the new providedIn attribute.
But how do we initialize a (root level singleton) service on demand, when certain criteria is met, while preserving tree shake-ability? The latter loads a video from assets and plays it, the former is only a landing page. - . If you don't want a application-wide singleton use the provider's array of a component instead. To do that, one way is to start a service that observes the navigation and store the last navigated url or something like that. -
We can send HTTP requests directly from the home component but thats not really the recommended way to do it here comes the role of Angular services. Yes in this case it will be only part of your lazy-loaded module/chunks. While the workaround proposed at Stack Overflow works, I find it sub-optimal compared to the solution presented by OP. Copyright 2010 - https://indepth.dev/posts/1151/a-deep-dive-into-injectable-and-providedin-in-ivy. All we need to do to make our services tree shakeable is to add `providedIn: root`, hence making it root provided/singleton service for the whole application. - All From a single slot machine in 1963 to being listed on Nasdaq Stockholm and holding gaming licenses in 18 jurisdictions, Betsson Group has come a long way. Create a new module named ProtectedResolversModule and use providedIn: ProtectedResolversModule and move the resolvers there. Well occasionally send you account related emails. we use server-side rendering and on the server side we dont want these features initialized, or used. Anyway, the main reason for me opening this issue is the fact that the documentation is misleading and should be more specific. I think Angular have made a bit of a mess of the providedIn syntax. Copyright 2022 IDQNA.COM. It seems to have confused a lot of people. RtmY, This is not good. I am used to repeating some facts because I want to be sure that it's understandable (better twice than once ) and it's my vice. The main issue is that maybe you want it to be started along with the application to grab useful information that you will need in the future when you instantiate some component that injects it. Load times are one of the most basic, most important, oldest KPIs of any webpage, especially for the first load time. It is actually not. If nothing is using such a service then why to have it in the code? A classic example is when you want to keep track of the last route the user visited on the app (or maybe the user navigation history during the last hour). At that moment, if you need your navigation history to go back to the last visited page, you won't have it because the service would have just been started at that time. It is not the same instance you used in other module. Since official (and widely followed) Angular policy is to use providedIn: 'root', I decided that on the whole it would be less confusing for other developers if I just stuck with this. Simon_Weaver, Disappointing indeed, although I have to say this hasn't caused me any issues thus far. They also tend to have all services waiting in the memory while you may not even use them ever. First of all we need a service to provide. "{ providedIn: 'root' }" does not instantiate services as documented. When you provide the service at the root level, Angular creates a single, shared instance of HeroService and injects into any class that asks for it. document.write(d.getFullYear()) DarkNeuron, That referenced comment got very badly voted down - plus the comment says "With tree shakeable providers, you now have zero reasons to provide a service from a module (there is a rare case on some lazy loaded services with a component using the service from a separate lazy module)." Already on GitHub? In the scenario mentioned, this service will be initialized, loaded into the memory and waiting to be called to load the video module. @HeeCheol-Kim really? We want to create an application with 2 screens, a home page and a video player page. - An Angular service is a TypeScript class that encapsulates a set of similar functionalities, like fetching data from a server, in your projects code. As a long-time user of various DI-containers, I also vouch for the idea of adding the eager: true flag for the @Injectable() decorator. Theres a new attribute in Angular 6 and you need to start using it. minigeek, @maxisam yes, you are right :). So being your average object-oriented Joe, I obviously ended up creating RouterEventHandlerService and isolating the event handling logic there. var d = new Date() the capital 'L' was the problem! https://dev.to/christiankohler/improved-dependeny-injection-with-the-new-providedin-scopes-any-and-platform-30bb. Heres where it all fits together. I've received 5 up-votes now for this answer, so I feel as though I ought to come clean and say that I'm no longer actually following my own advice on this (below)! Which one of them should i remove / change according to your solution? Dynamic third party loading solves issues which are dynamic in view of the application/module lifecycle, such as `we wont need the video player while the user is logged out`. the app root chunks.js or will this still lazy load the service and later make it a global singleton, when I lazy load that module. We might even use dynamic import for our ES6 modules (/packages) that we dont need immediately after loading its containing Angular module. Thanks! rights reserved. As is, the "Tour of Heroes"-doc is misleading. some message string elements in MessageService's constructor. Injector takes care of providing the services HlsLoaderService would have as dependency, without which we couldnt even access the root provided singleton, rather wed need to manually create one, while also manually passing through its dependencies. SPAs such as Angular apps tend to load all the routes code, including all third party packages you might only use later.