Why inject is needed in this situation?

[bakura10]

Hi :),

Sorry if this is a stupid question, but I am not understanding why I need to use an @Inject here. I am registering a MikroORM instance:

const orm = await MikroORM.init(config);

let container = new Container();
container.bind<MikroORM>(MikroORM).toConstantValue(orm);

container.resolve(Foo);

Where Foo is:

import {MikroORM} from "@mikro-orm/core";
import {inject, injectable} from "inversify";

@injectable()
export class Foo {
    constructor(manager: MikroORM) {
        console.log(manager);
    }
}

If I add @Inject(MikroORM) this works, but I fail to understand why. Isn't the container supposed to automatically resolve this as this is a class name ?

I'm coming from PHP background, so I still need to adjust my way to Typescript, but I spent a few hours failing to understand why it is not working here.

Thanks!

[Jameskmonger]

Hey @bakura10, TypeScript is "transpiled" to JavaScript, which is untyped, therefore it lacks the type information at runtime.

The transpiled class from your example will look something like:

class Foo {
    constructor(manager) {
        console.log(manager);
    }
}

Therefore the @inject is needed to attach the type information to the class at runtime.