This library implements dependency injection for javascript and typescript.
- Similar syntax to InversifyJS
- Can be used without decorators
- Less Features but straight forward
- Can bind dependencies as classes, factories and static values and provide dependencie arguments or parameters if needed
- Supports binding in singleton scope
- Cached - Resolves only once in each dependent class by default
- Cache can switched off directly at the inject decorator
- Made with unit testing in mind
- Supports dependency rebinding and container snapshots and restores
- Lightweight - Below 1kb brotli/gzip compressed
- Does NOT need reflect-metadata which size is around 50 kb
- 100% written in Typescript
npm install --save-dev @owja/iocLatest preview/dev version (alpha or beta)
npm install --save-dev @owja/ioc@nextThe container is the place where all dependencies get bound to. It is possible to have multiple container in our project in parallel.
import {Container} from "@owja/ioc";
const container = new Container();This is the default way to bind a dependency. The class will get instantiated when the dependency gets resolved. You will be able to pass down it's dependencie arguments once you resolve it.
container.bind<ServiceInterface>(symbol).to(Service);This will create only one instance of Service
container.bind<ServiceInterface>(symbol).to(Service).inSingletonScope();Factories are functions which will get called when the dependency gets resolved
container.bind<ServiceInterface>(symbol).toFactory(() => new Service());
container.bind<string>(symbol).toFactory(() => "just a string");
container.bind<string>(symbol).toFactory((a: string) => `I need a string parameter: ${a}`);A factory can configured for singleton scope too. This way will only executed once.
container.bind<ServiceInterface>(symbol).toFactory(() => new Service()).inSingletonScope();This is always like singleton scope, but it should be avoid to instantiate dependencies here. If they are circular dependencies, they will fail.
container.bind<ServiceInterface>(symbol).toValue(new Service()); // Bad, should be avoid
container.bind<string>(symbol).toValue("just a string");
container.bind<() => string>(symbol).toValue(() => "i am a function");This is the way how we can rebind a dependency while unit tests. We should not need to rebind in production code.
container.rebind<ServiceMock>(symbol).toValue(new ServiceMock());Normally this function is not used in production code. This will remove the dependency from the container.
container.remove(symbol);Getting dependencies without @inject decorators trough container.get() is only meant for unit tests.
This is also the internal way how the @inject decorator and the functions wire() and resolve() are getting the
dependency.
container.get<Interface>(symbol);To get a dependency without @inject decorator in production code use wire() or resolve(). Using container.get()
directly to getting dependencies can result in infinite loops with circular dependencies when called inside of
constructors. In addition container.get() does not respect the cache.
Important Note: You should avoid accessing the dependencies from any constructor. With circular dependencies this can result in a infinite loop.
This creates a snapshot of the bound dependencies. After this we can rebind dependencies and can restore it back to its old state after we made some unit tests.
container.snapshot();container.restore();To use the decorator you have to set experimentalDecorators to true
in your tsconfig.json.
First we have to create a inject decorator for each container:
import {createDecorator} from "@owja/ioc";
export const inject = createDecorator(container);Then we can use the decorator to inject the dependency.
class Example {
@inject(symbol/*, [tags], ...dependencie arguments*/)
readonly service!: Interface;
method() {
this.service.doSomething();
}
}If we do not want to use decorators, we can use the wire function. It does the same like the inject
decorator and we have to create the function first like we do with inject.
import {createWire} from "@owja/ioc";
export const wire = createWire(container);Then we can wire up the dependent to the dependency.
class Example {
readonly service!: Interface;
constructor() {
wire(this, "service", symbol/*, [tags], ...dependencie arguments*/);
}
method() {
this.service.doSomething();
}
}Notice: With
wire()the property, in this caseservice, has to be public.
A second way to resolve a dependency without decorators is to use resolve().
To use resolve() we have to create the function first.
import {createResolve} from "@owja/ioc";
export const resolve = createResolve(container);Then we can resolve the dependency in classes and even functions.
class Example {
private readonly service = resolve<Interface>(symbol);
method() {
this.service(/*...dependencie arguments*/).doSomething();
}
}function Example() {
const service = resolve<Interface>(symbol);
service(/*...dependencie arguments*/).doSomething();
}Notice: We access the dependency trough a function. The dependency is not assigned directly to the property/constant. If we want direct access we can use
container.get()but we should avoid usingget()inside of classes because we then loose the lazy dependency resolving/injection behavior and caching.
Symbols are used to identify our dependencies. A good practice is to keep them in one place.
export const TYPE = {
"Service" = Symbol("Service"),
// [...]
}Symbols can be defined with Symbol.for() too. This way they are not unique.
Remember Symbol('foo') === Symbol('foo') is false but
Symbol.for('foo') === Symbol.for('foo') is true
export const TYPE = {
"Service" = Symbol.for("Service"),
// [...]
}Since 1.0.0-beta.3 we use the symbol itself for indexing the dependencies. Prior to this version we indexed the dependencies by the string of the symbol.
With version 2 we added the possibility to use a type-safe way to identify our dependencies. This is done with tokens:
export TYPE = {
"Service" = token<MyServiceInterface>("Service"),
// [...]
}In this case the type MyServiceInterface is inherited when using container.get(TYPE.Service), resolve(TYPE.Service)
and wire(this, "service", TYPE.Service)and does not need to be explicitly added. In case of the decorator @inject(TYPE.Service) it needs to be added
but it throws a type error if the types don't match:
class Example {
@inject(TYPE.Service/*, [tags], ...dependencie arguments*/) // throws a type error because WrongInterface is not compatible with MyServiceInterface
readonly service!: WrongInterface;
}Correkt:
class Example {
@inject(TYPE.Service/*, [tags], ...dependencie arguments*/)
readonly service!: MyServiceInterface;
}Plugins are a way to hook into the dependency resolving process and execute code which can access the dependency and also the dependent object.
A plugin can add directly to a dependency or to the container.
container.bind(symbol).to(MyService).withPlugin(plugin);container.addPlugin(plugin);The plugin is a simple function which has access to the dependency, the target (the instance which requires the dependency), the arguments which are passed, the token or symbol which represents the dependency and the container.
type Plugin<Dependency = unknown> = (
dependency: Dependency,
target: unknown,
args: symbol[],
token: MaybeToken<Dependency>,
container: Container,
) => void;The following code is a plugin which links a preact view component to a service by calling forceUpdate every time the service executes the listener:
import {Plugin} from "@owja/ioc";
import {Component} from "preact";
export const SUBSCRIBE = Symbol();
export const serviceListenerPlugin: Plugin<Listenable> = (service, component, args) => {
if (args.indexOf(SUBSCRIBE) === -1 || !component) return;
if (!isComponent(component)) return;
const unsubscribe = service.listen(() => component.forceUpdate());
const unmount = component.componentWillUnmount;
component.componentWillUnmount = () => {
unsubscribe();
unmount?.();
};
};
function isComponent(target: unknown) : target is Component {
return !!target && typeof target === "object" && "forceUpdate" in target;
}
interface Listenable {
listen(listener: () => void): () => void;
}Note: this will fail on runtime if
servicedoes not implement theListenableinterface because there is no type checking done
This plugin is added to the dependency directly:
const TYPE = {
TranslationService: token<TranslatorInterface>("translation-service"),
};
container
.bind<TranslatorInterface>(TYPE.TranslationService)
.toFactory(translationFactory)
.inSingletonScope()
.withPlugin(serviceListenerPlugin);In a component it is then executed when the dependency is resolved:
class Index extends Component {
@inject(TYPE.TranslationService, [SUBSCRIBE]/*, ...dependencie arguments*/)
readonly service!: TranslatorInterface;
render() {
return (
<div>{this.service.t("greeting")}</div>
);
}
}This works also with wire and resolve:
class Index extends Component {
readonly service!: TranslatorInterface;
constructor() {
super();
wire(this, "service", TYPE.TranslationService, [SUBSCRIBE]/*, ...dependencie arguments*/);
}
[...]
}
class Index extends Component {
readonly service = resolve(TYPE.TranslationService, [SUBSCRIBE]/*, ...dependencie arguments*/);
[...]
}In case you add a plugin it is executed every time the dependency is resolved. If you want to prevent this you can
add the NOPLUGINS tag to the arguments:
import {NOPLUGINS} from "@owja/ioc";
class Example {
@inject(TYPE.MyService, [NOPLUGINS]/*, ...dependencie arguments*/)
readonly service!: MyServiceInterface;
}npm install --save-dev @owja/iocNow we create the folder services and add the new file services/types.ts:
export const TYPE = {
MyService: Symbol("MyService"),
MyOtherService: Symbol("MyOtherService"),
};Next we create out example services.
File services/my-service.ts
export interface MyServiceInterface {
hello: string;
}
export class MyService implements MyServiceInterface{
hello = "world";
}File services/my-other-service.ts
export interface MyOtherServiceInterface {
random: number;
}
export class MyOtherService implements MyOtherServiceInterface {
random = Math.random();
}Next we need a container to bind our dependencies to. Let's create the file services/container.ts
import {Container, createDecorator} from "@owja/ioc";
import {TYPE} from "./types";
import {MyServiceInterface, MyService} from "./service/my-service";
import {MyOtherServiceInterface, MyOtherService} from "./service/my-other-service";
const container = new Container();
const inject = createDecorator(container);
container.bind<MyServiceInterface>(TYPE.MyService).to(MyService);
container.bind<MyOtherServiceInterface>(TYPE.MyOtherService).to(MyOtherService);
export {container, TYPE, inject};Lets create a example.ts file in our source root:
import {TYPE, inject} from "./service/container";
import {MyServiceInterface} from "./service/my-service";
import {MyOtherServiceInterface} from "./service/my-other-service";
class Example {
@inject(TYPE.MyService/*, [tags], ...dependencie arguments*/)
readonly myService!: MyServiceInterface;
@inject(TYPE.MyOtherService/*, [tags], ...dependencie arguments*/)
readonly myOtherService!: MyOtherServiceInterface;
}
const example = new Example();
console.log(example.myService);
console.log(example.myOtherService);
console.log(example.myOtherService);If we run this example we should see the content of our example services.
The dependencies (services) will injected on the first call. This means if you rebind the service after
accessing the properties of the Example class, it will not resolve a new service. If you want a new
service each time you call example.myService you have to add the NOCACHE tag:
// [...]
import {NOCACHE} from "@owja/ioc";
class Example {
// [...]
@inject(TYPE.MyOtherSerice, NOCACHE/*, ...dependencie arguments*/)
readonly myOtherService!: MyOtherServiceInterface;
}
// [...]In this case the last two console.log() outputs should show different numbers.
For unit testing we first create our mocks
test/my-service-mock.ts
import {MyServiceInterface} from "../service/my-service";
export class MyServiceMock implements MyServiceInterface {
hello = "test";
}test/my-other-service-mock.ts
import {MyOtherServiceInterface} from "../service/my-other-service";
export class MyOtherServiceMock implements MyOtherServiceInterface {
random = 9;
}Within the tests we can snapshot and restore a container. We are able to make multiple snapshots in a row too.
File example.test.ts
import {container, TYPE} from "./service/container";
import {MyServiceInterface} from "./service/my-service";
import {MyOtherServiceInterface} from "./service/my-other-service";
import {MyServiceMock} from "./test/my-service-mock";
import {MyOtherServiceMock} from "./test/my-other-service-mock";
import {Example} from "./example";
describe("Example", () => {
let example: Example;
beforeEach(() => {
container.snapshot();
container.rebind<MyServiceInterface>(TYPE.MyService).to(MyServiceMock);
container.rebind<MyOtherServiceInterface>(TYPE.MyOtherService).to(MyOtherServiceMock);
example = new Example();
});
afterEach(() => {
container.restore();
});
test("should return \"test\"", () => {
expect(example.myService.hello).toBe("test");
});
test("should return \"9\"", () => {
expect(example.myOtherService.random).toBe(9);
});
});Current state of development can be seen in our Github Projects.
This library is highly inspired by InversifyJS but has other goals:
- Make the library very lightweight (less than one kilobyte)
- Implementing less features to make the API more straight forward
- Always lazy inject the dependencies
- No meta-reflect required
MIT
Copyright Β© 2019-2022 The OWJA! Team
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