@woubuc/inject
v1.0.1
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Dead-simple dependency injection library
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Dependency Injection Container
A simple global dependency injection container
Basic usage
Simply annotate a service with @injectable()
to register it.
Use the inject()
function to get the singleton instance of the service. The
DI container will automatically construct an instance of the injected class
the first time it is injected anywhere.
import { injectable, inject } from '@woubuc/inject';
@injectable()
class MyService {
doStuff() {}
}
class OtherService {
private readonly service = inject(MyService);
public doStuff() {
this.service.doStuff();
}
}
Custom tokens
You can use strings or symbols as injection tokens, instead of classes.
import { inject, injectable } from '@woubuc/inject';
const token = 'foo';
@injectable({ token })
class MyService {
doStuff() {}
}
class OtherService {
private readonly service = inject<MyService>(token);
public doStuff() {
this.service.doStuff();
}
}
Note: always prefer class injection tokens as they are automatically strongly typed.
The DI Container
You can get a reference to the current container with Container.current()
.
This allows you to do more dynamic things with the container, besides simply
injecting.
Get (inject)
The simple inject()
function is actually shorthand for
Container.current().get()
:
import { Container, injectable } from '@woubuc/inject';
@injectable()
class MyService {
doStuff() {}
}
class OtherService {
private readonly service = Container.current().get(MyService); // The long version
public doStuff() {
this.service.doStuff();
}
}
Provide
Use provide()
to provide custom data for a given injection token. Combined
with string tokens, this can be used to provide e.g. configuration values.
import { Container, inject } from '@woubuc/inject';
const urlToken = Symbol('urlToken');
Container.current().provide(urlToken, 'http://example.com/');
class MyApiClientService {
private readonly url = inject<string>(urlToken);
public async load() {
await fetch(this.url);
}
}
Example: mocking injectables
You can use provide()
to provide mock classes for tests.
// Main app
import { inject, injectable } from '@woubuc/inject';
@injectable()
class ApiService {
public get() {
return fetch('http://example.com');
}
}
@injectable()
class TestableService {
private api = inject(ApiService);
public async load() {
this.api.get(); // Does a fetch request
}
}
//
// In your tests:
//
import { Container } from './lib.js';
test('my test', (t) => {
class MockApiService {
public get() {
return {}; // Doesn't do a fetch request
}
}
// Provide the mock implementation
Container.current().provide(ApiService, new MockApiService());
inject(TestableService).load(); // Doesn't do fetch request when calling api.get()
});
Scoped containers
Use scoped()
to create a scoped child container and run (async) logic in it.
import { Container, inject } from '@woubuc/inject';
// Inject (and instantiate) an injectable in the global container
inject(MyService);
// Run some code in a local scoped container
await Container.current().scoped('temp-0', () => {
// When we ask for the same class, the container will see that an instance
// of it exists in the parent container (global) and return that instance.
inject(MyService);
// When we ask for a class that isn't instantiated yet, a new instance will
// be created in the current container scope.
inject(OtherService);
});
// Trying to inject the other service in the global container, even after
// injecting it successfully in the scoped container, will create a new instance
// because the global container has no idea what happened in the scoped container.
inject(OtherService);
Optional injectables
When using scoped()
and/or provide()
, sometimes you may have services that
might or might not exist (yet). In that case you can use injectOptional()
(or
Container.current().tryGet()
) to return undefined
if no instance of the
injectable exists yet - instead of constructing a new instance.
import { Container, injectOptional } from '@woubuc/inject';
const token = 'foo';
injectOptional(token); // undefined
Container.current().provide(token, 'hello world');
injectOptional(token); // 'hello world'
Destructors
If you need to run some cleanup logic when an instance is no longer needed
(particularly useful when working with scoped containers), you can implement the
OnDestroy
interface.
import { Container, inject, injectable, type OnDestroy } from '@woubuc/inject';
@injectable()
class MyService implements OnDestroy {
public constructor() {
console.log('hello');
}
public onDestroy() {
console.log('bye');
}
}
await Container.current().scoped('test', () => {
let service = inject(MyService); // "hello"
// We're at the end of the scope so the container is deleted
// and all local injectable instances are cleared.
// "bye"
});