Yet another Dependency Injection Library for JavaScript
Highly inspired by Autofac.NET
We have tried to accommodate all the best DI and IoC practices for JavaScript
const di = new Di;
☰
1
Registration
The greatest challenge for DI frameworks in JavaScript is to get the list of dependencies for a constructor, method, etc. JavaScript is not statically typed, so here other ways should be found to declare the dependencies. And we also try to follow the 1st rule of any di framework - "Your classes should not be dependent on the DI itself"
.
Though you can use it as a Service Locator
When registering the component, you specify identifiers, by which the dependency is resolved. It can be some another Type
, string identifier. But we do not encourage you to use string identifiers.
It is also possible to get the instance without having previously to register the Type
const foo = di.resolve(Foo);
Later you can register another Type for this one.
1.1
Type
Class
constructor;
class Foo {
constructor (bar, qux) {}
}
1.2
Instance
Pass already instantiated class to the container, and it will be used by all dependents
di.registerInstance(new Foo(di.resolve(IBar), di.resolve(IQux))).as(IFoo);
di.registerInstance(IBar, IFoo, (bar, foo) => new Foo(bar, foo)).as(IFoo);
di.registerInstance(IBar, IFoo, Foo).as(IFoo);
1.3
Factory
Register a function
which will create the instance on demand. Is similar to instance initializer, but the factory is called every time the dependency is required.
di.registerFactory(IBar, (bar) => {}).as(IFoo);
di.registerFactory(di => {}).as(IFoo);
2
Dependency definitions
2.1
Constructor
2.1.1
External definitions
From the previous paragraph you have already seen using
method, when registering the Type
. Here we define what identifiers should be used to instantiate the instance.
✨ Pros: Your implementation is fully decoupled from the DI and the registration itself.
class Foo {
constructor (logger) { logger.log() }
}
class Bar {
log (...args) { console.log(...args) }
}
class ILog { log () {} }
di
.registerType(Bar)
.as(ILog);
di
.registerType(Foo)
.using(ILog)
.asSelf()
.onActivated(foo => console.log(foo));
2.1.2
Decorators
✨ Pros: In-place configuration, but has reference to the di instance
class Foo {
constructor (@di.inject(ILog) logger) {
logger.log()
}
}
2.1.3
Default parameters
✨ Pros: new Foo()
also works
class Foo {
constructor (logger = di.resolve(ILog)) {
logger.log()
}
}
2.1.4
In-place meta information
Maybe most irrelevant feature, but anyway
✨ Pros: Your implementation is decoupled from the DI, but holds meta information for the DI library.
Per default we read the static $inject
property on the Type
class Foo {
static $constructor = [ ILog ]
constructor (logger) { logger.log() }
}
You can override the reader and provide us with the Identifiers for injection.
const CustomMetaReader = {
getConstructor (Type) {
return Type.$inject;
}
};
di.defineMetaReader(CustomMetaReader);
class Foo {
static $inject = [ILog]
constructor (logger) { logger.log() }
}
2.1.5
Other ways
💬 Do you have any ideas? Please share them via issues.
TypeScript: initially, this project targets plain JavaScript, but TypeScript is preferred.
2.2
Properties
Property injections are supported by Type
s components.
2.2.1
External definitions
class Foo {
constructor () {
this.logger = new DummyLogger();
}
doSmth () {
this.logger.log();
}
}
di
.registerType(Foo)
.properties({
logger: ILog
})
.asSelf();
2.2.2
In-place meta information
Per default we read the static $properties
to get the key: Identifier
information.
class Foo {
constructor () { }
}
Foo.$properties = {
logger: ILog
};
di
.registerType(Foo)
.asSelf();
You can override the reader and provide us with the Identifiers for injection.
let CustomMetaReader = {
getProperties (Type) {
}
};
di.defineMetaReader(CustomMetaReader);
2.2.3
Other ways
💬 Ideas about better API - please share!
2.3
Methods
Injections into Type
_s_functions.
2.3.1
External definitions
class Foo {
doSmth (logger) {
logger.log();
}
}
di
.registerType(Foo)
.methods({
doSmth: [ILog]
})
.asSelf();
2.3.2
In-place meta information
Per default we read the static $methods
with key:[Identifier, ...]
information.
class Foo {
doSmth (logger) { logger.log() }
static $methods = {
doSmth: [ ILog ]
};
}
di
.registerType(Foo)
.asSelf();
You can override the reader and provide us with the Identifiers for injection.
const CustomMetaReader = {
getMethods (Type) {
}
};
di.defineMetaReader(CustomMetaReader);
2.3.3
Other ways
💬 Ideas about better API - please share!
3
Consume
3.1
Initialize registered components
We inject all dependencies and return ready to use component.
let x = di.resolve(IFoo);
3.2
Create inherited classes
The inherited class accepts empty constructor, in this case we will pass the resolved components to the base class.
let FooWrapper = di.wrapType(IFoo);
let foo = new FooWrapper();
3.3
Create function delegates
Define function argument identifiers, and you can call the function without arguments.
let myFunction = di.wrapFunction(IFoo, IBar, (foo, bar) => {});
myFunction();
4
Additional configuration
4.1
Predefine parameter values
Sometimes it is needed to set values for parameters, which will be directly passed inside the function.
class Foo {
constructor (bar, shouldDoSmth)
}
di
.registerType(Foo)
.using(Bar)
.withParams(null, true)
1️⃣ Passing null values says the di library to resolve values from container by declared Type
2️⃣ Boolean true
from sample just shows the idea of passing values. You may want to get the value from app configuration or some other source.
4.2
Configurate arguments
Arguments or values for a constructor/function are resolved from 3 sources:
- Declared parameter values
- Type definitions
- Direct values from the current function call.
With options "ignore" "extend" "override"
you can control how we handle the third source. Default is "override"
5
How do we use the library?
We rarely use all of those registration and configuration features.
- All the
Services
, Workers
, Handlers
, Factories
- actually everything except Data Models
- we use mostly as singletons. Means any initialization of an Instance we do via di.resolve
. Note, that no configuration or registration is required - when nothing specified di initializes the class as-is.
We do this, while a class can memoize
initialization, data, configuration, or method calls.
import { UserService } from './UserService'
let service = di.resolve(UserService);
- To have more clear dependency tree structure, we define some dependencies via constructor as default parameters:
import { UserService } from './UserService'
class Foo {
constructor (
private service = di.resolve(UserService)
)
}
- For multiple implementations we use abstract classes.
abstract class AFoo {
abstract log ()
}
@di.for(AFoo)
class SomeFoo extends AFoo () {}
di.registerType(AFoo).for(AFoo)
class UserService {
constructor (
foo = di.resolve(AFoo)
) {}
}
class UserService {
constructor (
@di.inject(AFoo) foo: AFoo
){}
}
🏁
©️ MIT — 2021 Atma.js Project