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docs: Update dependency-injection-context.md (#55455)

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Kirk Larkin
2024-04-21 19:52:10 +01:00
committed by Alex Rickabaugh
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adev/src/content/guide/di/dependency-injection-context.md
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# Injection context
The dependency injection (DI) system relies internally on a runtime context where the current injector is available.
This means that injectors can only work when code is executed in this context.
This means that injectors can only work when code is executed in such a context.
The injection context is available in these situations:
* Construction (via the `constructor`) of a class being instantiated by the DI system, such as an `@Injectable` or `@Component`.
* During construction (via the `constructor`) of a class being instantiated by the DI system, such as an `@Injectable` or `@Component`.
* In the initializer for fields of such classes.
* In the factory function specified for `useFactory` of a `Provider` or an `@Injectable`.
* In the `factory` function specified for an `InjectionToken`.
* Within a stack frame that is run in a injection context.
* Within a stack frame that runs in an injection context.
Knowing when you are in an injection context, will allow you to use the [`inject`](api/core/inject) function to inject instances.
Knowing when you are in an injection context will allow you to use the [`inject`](api/core/inject) function to inject instances.
## Class constructors
Everytime the DI system instantiates a class, this is done in an injection context. This is being handled by the framework itself. The constructor of the class is executed in that runtime context thus allowing to inject a token using the [`inject`](api/core/inject) function.
Every time the DI system instantiates a class, it does so in an injection context. This is handled by the framework itself. The constructor of the class is executed in that runtime context, which also allows injection of a token using the [`inject`](api/core/inject) function.
<docs-code language="typescript" highlight="[[3],[6]]">
class MyComponent {
@@ -30,7 +30,7 @@ class MyComponent {
## Stack frame in context
Some APIs are designed to be run in an injection context. This is the case, for example, of the router guards. It allows the use of [`inject`](api/core/inject) to access a service within the guard function.
Some APIs are designed to be run in an injection context. This is the case, for example, with router guards. This allows the use of [`inject`](api/core/inject) within the guard function to access a service.
Here is an example for `CanActivateFn`
@@ -43,8 +43,8 @@ const canActivateTeam: CanActivateFn =
## Run within an injection context
When you want to run a given function in an injection context without being in one, you can do it with `runInInjectionContext`.
This requires to have access to a given injector like the `EnvironmentInjector` for example.
When you want to run a given function in an injection context without already being in one, you can do so with `runInInjectionContext`.
This requires access to a given injector, like the `EnvironmentInjector`, for example:
<docs-code header="src/app/heroes/hero.service.ts" language="typescript"
highlight="[9]">
@@ -66,7 +66,7 @@ Note that `inject` will return an instance only if the injector can resolve the
## Asserts the context
Angular provides `assertInInjectionContext` helper function to assert that the current context is an injection context.
Angular provides the `assertInInjectionContext` helper function to assert that the current context is an injection context.
## Using DI outside of a context