re: Dependency injection in TypeScript applications powered by InversifyJS VIEW POST

VIEW PARENT COMMENT VIEW FULL DISCUSSION

Thanks! Good question, InversifyJS allows you to have more control over the life-cycle of dependencies and how the dependency graph is composed than a dictionary of singletons. InversifyJS gives you more power thanks to 3 main features:

Scopes

At the moment the core library allows:

  • Transient scope (one instance each time you call container.get())
  • Singleton scope (same instance for every call to container.get())

I'm working on custom scopes which will allow singletons within a context as opposed to application-level singletons. This will enable things like "Request scope" which can be used to declare singletons at HTTP-request-level.

Contextual constraints

You can inject dependencies based on execution time constraints. InversifyJs supports many types of constraints:

interface BindingWhenSyntax<T> {
    when(constraint: (request: interfaces.Request) => boolean): interfaces.BindingOnSyntax<T>;
    whenTargetNamed(name: string): interfaces.BindingOnSyntax<T>;
    whenTargetTagged(tag: string, value: any): interfaces.BindingOnSyntax<T>;
    whenInjectedInto(parent: (Function|string)): interfaces.BindingOnSyntax<T>;
    whenParentNamed(name: string): interfaces.BindingOnSyntax<T>;
    whenParentTagged(tag: string, value: any): interfaces.BindingOnSyntax<T>;
    whenAnyAncestorIs(ancestor: (Function|string)): interfaces.BindingOnSyntax<T>;
    whenNoAncestorIs(ancestor: (Function|string)): interfaces.BindingOnSyntax<T>;
    whenAnyAncestorNamed(name: string): interfaces.BindingOnSyntax<T>;
    whenAnyAncestorTagged(tag: string, value: any): interfaces.BindingOnSyntax<T>;
    whenNoAncestorNamed(name: string): interfaces.BindingOnSyntax<T>;
    whenNoAncestorTagged(tag: string, value: any): interfaces.BindingOnSyntax<T>;
    whenAnyAncestorMatches(constraint: (request: interfaces.Request) => boolean): interfaces.BindingOnSyntax<T>;
    whenNoAncestorMatches(constraint: (request: interfaces.Request) => boolean): interfaces.BindingOnSyntax<T>;
}

You can do something like:

container.bind<Weapon>("Weapon").to(Katana).whenInjectedInto(Samurai);
container.bind<Weapon>("Weapon").to(Shuriken).whenInjectedInto(Ninja);

Interception

InversifyJS allows you to implement interception thanks to the onActivation handlers and the @postConstruct decorator. You can learn more about IoC and interception here.

Great. I suppose this fine level of control will suit more to backend applications or really complex web apps with lots of services when you need something more customizable.

Yes, InversifyJS becomes more valuable as your application grows.

code of conduct - report abuse