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Discussion on: Dependency injection in TypeScript applications powered by InversifyJS

theodesp profile image
Theofanis Despoudis • Edited

Great Work Remo,
What are the advantages you think of this library and for example just using a dictionary or a Map of singleton objects that you can pass on to constructors? Something like a Registry Pattern.
Its just I find the decorators in classes to be associated with mixins and I don't find that very appealing

remojansen profile image
Remo H. Jansen Author • Edited

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:


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>;
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You can do something like:

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

theodesp profile image
Theofanis Despoudis

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.

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remojansen profile image
Remo H. Jansen Author

Yes, InversifyJS becomes more valuable as your application grows.

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