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How do I lazy load a service in Angular?
Angular’s service-specific API is injectAsync. It accepts a loader function, commonly one that uses a dynamic import(), and returns a function you can call when the feature needs the service. Invoking that function triggers the load by default; Angular then resolves the service through dependency injection.
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import { injectAsync } from '@angular/core';
const getExporter = injectAsync(
() => import('./report-exporter').then((m) => m.ReportExporter),
);
// Call this when the user requests an export:
const exporter = await getExporter();
This example assumes ReportExporter is auto-provided, such as with @Injectable({providedIn: 'root'}) or @Service(). Angular’s lazy-loading services guide says the service must be auto-provided for this pattern to work.
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Optionally prefetch the service
If you can anticipate a feature request, Angular’s guide also documents a prefetch trigger such as onIdle. Prefetching starts the download when its trigger resolves; if the user requests the service first, calling the loader starts the load then. Treat prefetching as an opportunity to shift when the request happens, not as a guarantee that the service is already available.
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What is the difference between lazy-loading a service and a route?
These approaches defer different code and are triggered at different boundaries:
| Approach | What is deferred | When loading starts | Typical use |
|---|---|---|---|
injectAsync |
A service dependency | When the returned loader function is invoked, or earlier if its prefetch trigger resolves | An infrequent feature or a service that depends on a large library |
loadComponent |
A route component | When the user visits the corresponding route | A page or route component that need not be in the initial route bundle |
loadChildren |
Child route definitions and their associated code | When the user visits the corresponding route | A separately loaded group of child routes |
Angular’s router commonly uses dynamic imports with loadComponent and loadChildren. It fetches the resulting chunks when the user visits the corresponding route. The lazy-loaded routes guide also explains that the router runs these loader functions in the current route’s injection context. A route loader can therefore use inject to access providers declared on that route, inherited from parent routes, or available globally.
A route can be lazy-loaded while one of its services is not independently deferred, or a service can be deferred without making its route lazy. Choose the API based on which code should wait: the service dependency, the route component, or the child routes.
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Choose the provider scope according to which parts of the application need to inject the service. Deferring a service’s code and deciding where its instance is available are related decisions, but they are not the same thing.
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| Provider scope | Where it is available | Best fit |
|---|---|---|
providedIn: 'root' or @Service() |
Application-wide through the root injector; Angular documents this as a shared singleton | A service used across feature areas or where the application needs a shared instance |
Route-level providers |
The route and its descendants, including their components, directives, guards, and resolvers | Feature-specific services, lazy-loaded dependencies, or route-specific configuration |
Route-level providers create a child injector. A service provided there is not available to eager application areas that use a different injector. If a component outside the route subtree tries to inject that service, provide it at a scope that component can access—often the root—or move the consumer into the route subtree. Angular’s provider guide describes application/bootstrap providers and route providers and their intended scopes.
Route scope does not automatically mean cleanup on navigation
By default, Angular’s route injector and its services persist after navigating away from that route and are not destroyed until the application closes. Route providers therefore define availability and scope, not a promise of immediate memory cleanup. Custom route behavior is needed for automatic cleanup. See Angular’s dependency-injection troubleshooting guide.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When is lazy loading worth using?
Lazy loading can reduce the JavaScript requested during the initial load, but it can also add requests later. It is most useful when code is not needed immediately—for example, an infrequent feature—or when a service depends on a large library. If users need the feature right away, deferring its code may simply postpone work and add a loading delay.
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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problems- Consider eager loading for primary landing pages; Angular’s performance guidance recommends it in general.
- Lazy-load less frequently visited pages or features where delaying their code is useful.
- Avoid building up multiple levels of nested lazy loading without considering the extra requests and their effect on performance.
- Do not assume a particular bundle-size reduction or performance improvement: the result depends on your app’s code, usage patterns, and loading conditions.
Angular’s route performance guidance discusses the trade-off between a smaller initial load and later requests. Its services guide covers the separate service-loading boundary.
How should I choose the API?
- Use
injectAsyncwhen the service itself should be loaded only when a feature calls for it. - Use
loadComponentorloadChildrenwhen the route component or child-route code should wait until navigation. - Use root provision for application-wide availability; use route providers when access should be limited to a route subtree or when configuration is route-specific.
- Check the Angular version used by your project before relying on version-sensitive API details; the official guides and API reference are the authoritative places to confirm current behavior.
For the service decorators and their provider options, see Angular’s services guide and Injectable API reference.
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