Binding

Binding is the registration of your services into your dependency injection (DI) container.

Auto-binding

The easiest way to register your class for automatic dependency injection, is by applying the @injectable() decorator to your class:

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

@injectable()
class FooService {
  // ...
}

This will automatically bind FooService as a singleton service. To request it from your service, you can use the .get() method on the container:

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

const container = new Container();
const fooService = container.get(FooService);
//    ^? Type will be inferred as `FooService`

• Its construction is lazy: it will only be created when you request it from the container.
• It is also a singleton: the first time a FooService is injected, a new instance is constructed, but it will reuse this instance whenever it needs to be injected again.

NOTE

Since Needle DI uses native ECMAScript TC39 decorators (which is currently in stage 3), you will need to transpile your code in order to use it in a browser or in Node.JS.

All modern transpilers (including TypeScript, esbuild, Webpack, Babel) do have support for stage 3 decorators. If you don't want to depend on transpilation, you can bind your services manually instead, without using decorators.

Manual binding

If you don't want to use the @injectable() decorator, for example if you don't want to use decorators or you want to bind a class that you cannot decorate (from another library), you can manually register your service with the .bind() method:

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

const container = new Container();

container.bind(FooService);

const fooService = container.get(FooService);
//    ^? Type will be inferred as `FooService`

This is the same as applying a decorator to FooService.

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There are many different ways to bind services, check out the section about providers to learn more.