Multi-injection

By default, when you bind an existing token again, it will overwrite any previous binding.

However, it is also possible to register multiple values for the same token:

import { Container } from "@needle-di/core";

const container = new Container();

container.bind({
  provide: FooService,
  multi: true,
  factory: () => new FooService(123, "abc"),
});

container.bind({
  provide: FooService,
  multi: true,
  factory: () => new FooService(456, "def"),
});

To inject both instances, you can pass { multi: true } to the inject() function:

class MyService {
  constructor(
    private fooServices = inject(FooService, { multi: true }),
    //      ^? Type will be inferred as `FooService[]`
  ) {}
}

Behaviour & limitations

There are some rules associated with multi-providers:

• It is not allowed to combine multiple providers for the same token with both multi: false and multi: true.
• When you specify only one provider with multi: true, it is still allowed to inject it as a single instance.
• When you specify multiple providers with multi: true, it will throw an error when you try to inject a single instance.
• When you try to inject with multi: true and optional: true, and there are no providers, it will still return undefined instead of an empty array.