Context

The context is a special object that binds a set of services altogether. It is primarly existed to limit the existance of a service or set of services.

Imagine in an express app, each time the user requests the server you create a context to limit all service with Scoped lifetime to it, and after responding to that request, you remove the context so all services are removed. for instance, there's an internal context used to group all singleton services, what made them singleton is that the context will live throughout the application lifetime.

Create Context#

• A Context can be created using Create() method.

@Injectable({
	lifetime: ServiceLifetime.Scoped,
})
class Logger {}

const context = Injector.Create();
const logger = Injector.GetRequiredService(Logger, context);

// Remove the context and everything bound to it.
Injector.Destroy(context);

The above sample creates a context and used it to return an instance of Logger type, when the context is no longer needed you have to destroy it to free up the memory.

• Using CreateScope()

The other way is to use CreateScope() which simplifies the consumption of Scoped services.

CreateScope takes function that provide the context as argument. the function could be void or promise

@Injectable({
	lifetime: ServiceLifetime.Scoped,
})
class Logger {}

Injector.CreateScope((context) => {
	const logger = Injector.GetRequiredService(Logger, context);
});

In this sample, the context created internally and provided as argument, the Injector.GetRequiredService method used to request a Logger instance.

the Destroy method is no longer needed since it will be called internally immediately after the function execution is done.

const context = Injector.Create();

const logger = Injector.GetRequiredService(Logger, context);
// equivalent to
Injector.GetRequiredService(serviceType, context);

Context Extras#

A context can holds extras which you could use to store additional data

const context = Injector.Create();

context.setExtra("data", {});

context.getExtra("data");

it's most useful when you want to store some data at the creation of context and use it later on when requesting or registering a service.

Summary#

1. Think of Context as map that store service.

2. All singleton services are managed interally by a context.

3. There's two way you can create context, using Create or CreateScope.

4. If you created a context using Create make sure to destroy it.

5. The intention of Context Extras as to store data from and transfer it from scope to another and not to store any dependencies.