pumpit

v10.1.0

Published

15 days ago

Dependency injection container without decorators, supports circular dependencies and arrays of dependencies.

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ioc di dependency injection dependency inversion dependency injection container inversion of control container

PumpIt

PumpIt is a small (~2KB) dependency injection container without the decorators and zero dependencies, suitable for the browser. It supports different injection scopes, child containers, hooks etc...

Motivation

Dependency injection is a powerful concept, and there are some excellent solutions like tsyringe, awilix, and inversify, however, they all use decorators (which are great, but not a standard), and their file size is not suitable for front-end development. So I've decided to create an implementation of a dependency injection container that is small and doesn't use decorators. I also believe that I've covered all the functionality of the above-mentioned libraries.

Getting Started

Installation:

npm i pumpit

Since PumpIt does not rely on the decorators the injection is done via the injection property. When used with classes, inject will be a static property on the class, and it will hold an array of registered injection tokens that will be injected into the constructor in the same order when the class instance is created (in case of factory functions it will be a property on the function itself, more on that later).

Registering classes

import { PumpIt } from 'pumpit'

const container = new PumpIt()
const bindKeyB = 'b'

class TestA {
  static inject = [bindKeyB]

  constructor(b: B) {}
}

class TestB {}

// bind (register)  classes to the injection container.
container.bindClass(TestA, TestA).bindClass(bindKeyB, TestB)

//resolve values
const instanceA = container.resolve<TestA>(TestA)
const instanceB = container.resolve<TestA>(bindKeyB)

instanceA.b // injected B instance

There is also alternative syntax that you can use when you don't want to use the static inject property, or you are importing a class from third-party packages.

import { PumpIt } from 'pumpit'

const container = new PumpIt()
class TestA {
  constructor(b: TestB) {}
}

class TestB {}

//`bind`(register)  class to the injection container.
container.bindClass(TestA, { value: TestA, inject: [TestB] })
//or
container.bindClass('some_key_to_bind', { value: TestA, inject: [TestB] })

You can also use a special INJECT_KEY value (which is actually a Symbol) to inject the dependencies, this also helps when you can't use a static inject property on a class (maybe the property already exists or it's a third party class)

import { PumpIt, INJECT_KEY } from 'pumpit'

const container = new PumpIt()

class TestB {}

class TestA {
  static [INJECT_KEY] = [TestB]
  constructor(b: TestB) {}
}

//or you can also use this
TestA[INJECT_KEY] = [TestB]

container.bindClass(TestA,TestA)
container.bindClass(TestB,TestB)

Class injection inheritance

Class injection inheritance is supported out of the box, which means that the child class will get dependencies that are set to be injected to the parent.

const pumpIt = new PumpIt()

class TestB {}

class TestA {
  static inject = [TestB]
}

class TestC extends TestA {
  //TestB will be injected by reading `inject` array from the parent (TestA)
  constructor(public b: TestB) {
    super()
  }
}

pumpIt.bindClass(TestA, TestA)
pumpIt.bindClass(TestB, TestB)
pumpIt.bindClass(TestC, TestC)

const instance = pumpIt.resolve<TestC>(TestC)

expect(instance.b).toBeInstanceOf(TestB)

Combining injection dependencies

Child class can define their own dependencies and combine them with the parent dependencies.

class TestB {}
class TestD {}

class TestA {
  static inject = [TestB]

  constructor(public b: TestB) {}
}

class TestC extends TestA {
  // use dependencies from the parent and add your own (TestD class)
  static inject = [...TestA.inject, TestD]

  constructor(
    public b: TestB,
    public d: TestD
  ) {
    super()
  }
}

pumpIt.bindClass(TestA, TestA)
pumpIt.bindClass(TestB, TestB)
pumpIt.bindClass(TestC, TestC)
pumpIt.bindClass(TestD, TestD)

const instance = pumpIt.resolve<TestC>(TestC)

expect(instance.b).toBeInstanceOf(TestB)
expect(instance.d).toBeInstanceOf(TestD)

Registering factories

When registering function factories, function needs to be provided as the value, and when that value is requested, the function will be executed and returned result will be the value that will be injected where it is needed.

const container = new PumpIt()

const myFactory = () => 'hello world'

container.bindFactory(myFactory, myFactory)

const value: string = container.resolve(myFactory)

value === 'hello world'

Factories can also have dependencies injected. They will be passed as the arguments to the factory function when it is executed.

const container = new PumpIt()
class A {
  hello() {
    return 'hello from A'
  }
}

const myFactory = (a: A) => {
  return a.hello()
}
myFactory.inject = [A]

container.bindClass(A, A)
container.bindFactory(myFactory, myFactory)

const value: string = container.resolve(myFactory) //hello from A

Or alternative syntax (same as class alternative syntax):

const container = new PumpIt()

class A {
  hello() {
    return 'hello from A'
  }
}

const myFactory = (a: A) => {
  return a.hello()
}

container.bindClass(A, A)
container.bindFactory(myFactory, { value: myFactory, inject: [A] })

const value: string = container.resolve(myFactory)
value === 'hello from A'

You can also use a special INJECT_KEY value (which is actually a Symbol) to inject the dependencies. This is not that much useful when working with factories, but it can be very useful when working with classes

import { PumpIt, INJECT_KEY } from 'pumpit'

const container = new PumpIt()
class A {
  hello() {
    return 'hello from A'
  }
}

const myFactory = (a: A) => {
  return a.hello()
}

myFactory[INJECT_KEY] = [A]

container.bindClass(A, A)
container.bindFactory(myFactory, myFactory)

const value: string = container.resolve(myFactory) //hello from A

I encourage you to experiment with factories because they enable you to return anything you want.

Registering values

Values should be used when you just want to get back the same thing that is passed in to be registered.

const container = new PumpIt()

const myConfig = { foo: 'bar' }

container.bindValue('app_config', myConfig)

const resolvedConfig = container.resolve('app_config')

resolvedConfig === myConfig

Resolving container data

When the container data is resolved, if the key that is requested to be resolved is not found, the container will throw an error.

const container = new PumpIt()

container.resolve('key_does_not_exist') // will throw

Injection tokens

Injection tokens are the values by which the injection container knows how to resolve registered data. They can be string, Symbol, or any object.

const container = new PumpIt()
const symbolToken = Symbol('my symbol')

class A {}

//bind to container
container.bindClass('my_token', A)
container.bindClass(symbolToken, A)
container.bindClass(A, A)

//resolve
container.resolve<A>('my_token')
container.resolve<A>(symbolToken)
container.resolve<A>(A)

//inject tokens
class B {
  static inject = [symbolToken, 'my_token', A]
  constructor(aOne: A, aTwo: A, aThree: A) {}
}

Injection scopes

There are four types of injection scopes:

Singleton

Once the value is resolved the value will not be changed as long as the same container is used.

In the next example, both A and B instances have the same instance of C

import { PumpIt, SCOPE } from 'pumpit'

container = new PumpIt()

class A {
  static inject = [C, B]
  constructor(
    public c: C,
    public b: B
  ) {}
}
class B {
  static inject = [C]
  constructor(public c: C) {}
}

class C {}

container.bindClass(A, A)
container.bindClass(B, B)
container.bindClass(C, C, { scope: SCOPE.SINGLETON })

// A -> B,C,
// B -> C
const instanceA = container.resolve(A)

//A and B share the same instance C
instanceA.c === instanceA.b.c

Transient

This is the default scope. Every time the value is requested, a new value will be returned (resolved). In the case of classes, it will be a new instance every time, in the case of factories, the factory function will be executed every time.

In the next example, both A and B instances will have a different C instance.

import { PumpIt, SCOPE } from 'pumpit'
container = new PumpIt()

class A {
  static inject = [C, B]
  constructor(
    public c: C,
    public b: B
  ) {}
}
class B {
  static inject = [C]
  constructor(public c: C) {}
}

class C {}

container.bindClass(A, A)
container.bindClass(B, B)
container.bindClass(C, C, { scope: SCOPE.TRANSIENT })

// A -> B,C,
// B -> C
const instanceA = container.resolve(A)

//C instance is created two times
//A and B have different instances of C
instanceA.c !== instanceA.b.c //C

Request

This is similar to the singleton scope except the value is resolved once per resolve request chain. Every new call to container.resolve() will create a new value.

import { PumpIt, SCOPE } from 'pumpit'

container = new PumpIt()

class A {
  static inject = [C, B]
  constructor(
    public c: C,
    public b: B
  ) {}
}
class B {
  static inject = [C]
  constructor(public c: C) {}
}

class C {}

container.bindClass(A, A)
container.bindClass(B, B)
container.bindClass(C, C, { scope: SCOPE.REQUEST })

const firstA = container.resolve(A)
const secondA = container.resolve(A)
firstA.c === firstA.b.c // A and B share C

secondA.c === secondA.b.c // A and B share C

secondA.c !== firstA.c //C from first request is different to the C from the second request

Container singleton

This scope is similar to the regular singleton scope, but in the case of child containers, the child container will create its version of the singleton instance.

In the next example, the child container will create its own version of the singleton instance.

import { PumpIt, SCOPE } from 'pumpit'

container = new PumpIt()
const childContainer = container.child()

class A {
  static count = 0
  constructor() {
    A.count++
  }
}

container.bindClass(A, A, { scope: SCOPE.CONTAINER_SINGLETON })

const parentOneA = container.resolve(A)
const parentTWoA = container.resolve(A)

parentOneA === parentTWoA
A.count === 1

const childOneA = childContainer.resolve(A)
const childTwoA = childContainer.resolve(A)

childOneA === childTwoA
A.count === 2

// parent and child have different instances
childOneA !== parentOneA

Injection scopes do not apply to bound values (bindValue)

Optional injections

Whenever the injection container can't resolve the requested dependency anywhere in the chain, it will immediately throw.

But you can make the dependency optional, and if it cant be resolved, the container will not throw, and undefined will be injected in place of the requested dependency. For this, you need to use the get() helper function.

import { PumpIt, get } from 'pumpit'

const container = new PumpIt()

class A {
  //make B optional dependency
  static inject = [get(B, { optional: true })]
  constructor(public b: B) {}
}
class B {}

//NOTE: B is NOT registered with the container
container.bindClass(A, A)

const instanceA = container.resolve(A)

instanceA.b // undefined

Circular dependencies

NOTE: Circular dependency functionality has been removed in version 6. If you want to use circular dependency you can use version 5

Injecting arrays

NOTE: Injecting array as a dependency has been removed in version 6. If you want to use this feature you can use version 5

Post construct method

If the class that is being constructed (resolved) has a "postConstruct" method defined it will be called automatically when the class instance is created, in the case of singleton instances it will be called only once. One more important thing about postConstruct method is that it will be called in the reverse order of the resolution chain. Please refer to this test for a concrete example

Removing values from the container

Registered values can be removed from the container. When the value is removed, trying to resolve the value will throw an error.

const container = new PumpIt()

container.bindValue('name', 'Mario')

container.unbind('name')

container.resolve('name') // throws error

Calling the dispose method

If the class has a method dispose() it will automatically be called on the disposed of value, but only if the value is a singleton.

Internally, the container will remove the value from its internal pool, and if the value was registered with the scope: singleton and the value has been resolved before (class has been instantiated or factory function executed). That means that the container holds an instance of the value, and it will try to call the dispose of method on that instance, or in the case of the factory, on whatever was returned from the factory.

const container = new PumpIt()

class TestA {
  static count = 0
  dispose() {
    TestA.count++
  }
}

pumpIt.bindClass(TestA, TestA, { scope: 'SINGLETON' })
pumpIt.unbind(TestA)

pumpIt.has(TestA) // false

TestA.count === 1

If you don't want to call the dispose method, pass false as the second parameter container.unbind(TestA, false)

Removing all the values from the container

You can remove all the values from the container by calling container.unbindAll(). This method will remove all the keys from the container, so the container will be empty. All the same, rules apply as for the container.unbind() method.

const container = new PumpIt()
const callDispose = true
container.unbindAll(callDispose)

Locking the container

If the container is locked that particular container can't accept new bindings or unbind the values already in the container. Locking the container does not affect child containers.

const container = new PumpIt()

class TestA {}
class TestB {}

container.bindClass(TestA, TestA)

container.lock()

container.isLocked() // returns true

container.bindClass(TestB,TestB) //throws error

container.unbind(TestA) //throws error

Child containers

Every container instance can create a child container. Or every container can set it's parent.

The child container is a new PumpIt instance that is connected to the parent container instance and it inherits all the values that are registered with the parent.

The great thing about the child container is that it can shadow the parent value by registering a value with the same key.

Shadowing values

The child container can have the same key as the parent, in that case when the value is resolved, the child container value will be returned.

const parent = new PumpIt()
const child = parent.child()
//or child = new Pumpit()
// child.setParent(parent)
const key = 'some_key'

class ParentClass {}
class ChildClass {}

parent.bindClass(key, ParentClass)

child.bindClass(key, ChildClass)

const instance = child.resolve(key) // ChildClass

Parent -> child chains can be as long as you like grand parent -> parent -> child ...

Checking for values

When you check if the value exists on the child, the parent instance is also searched. You can optionally disable searching on the parent.

const parent = new PumpIt()
const child = parent.child()

class TestA {}

parent.bindClass(TestA, TestA)

child.has(TestA) //true

// disable search on the parent
child.has(TestA, false) // false

Child singletons

If the parent container has registered a value with a scope SINGLETON all child containers will share the same instance however, if the parent has registered the value with the scope CONTAINER_SINGLETON then child containers will create their versions of singleton instances.

const parent = new PumpIt()
const child = parent.child()

class TestA {
  static count = 0

  constructor() {
    TestA.count++
  }
}

parent.bindClass(TestA, TestA, { scope: SCOPE.CONTAINER_SINGLETON })

const parentInstance = parent.resolve<TestA>(TestA)
const childInstance = child.resolve<TestA>(TestA)

parentInstance !== childInstance
TestA.count === 2

Validating bindings

Calling validate or validateSafe will validate the bindings in the container. It will check if all the dependencies that are required by other bindings are present in the container.

validate method will throw an error, while validateSafe will return a validation result. Calling these methods will not instantiate classes or run factory functions, so there is still a possibility that you will not get what you want when dependencies are resolved at runtime.

In the next example RequestTest class is not present in the container, but is needed in class TestB


const pumpIt = new PumpIt()

class TestA {}

class TestB {
  static inject = [TestA]

  constructor(
    public a: TestA,
  ) {}
}

//bind only TestB
pumpIt.bindClass(TestB, TestB)

const result = pumpIt.validateSafe()

expect(result).toEqual({
  valid: false,
  errors: [{ key: TestA, wantedBy: [TestB] }],
})

Helpers

Register injections

registerInjections helper function with a class or factory. It will automatically create inject property on the class or factory function.

test("use helper to inject in to class", () => {
  const pumpIt = new PumpIt()

  class TestA {}
  class TestB {}
  class TestC {
    constructor(
      public a: TestA,
      public b: TestB,
    ) {}
  }

  registerInjections(TestC, [TestA, TestB])

  pumpIt
    .bindClass(TestA, TestA)
    .bindClass(TestB, TestB)
    .bindClass(TestC, TestC)

  const result = pumpIt.resolve<TestC>(TestC)

  expect(result.a).toBeInstanceOf(TestA)
  expect(result.b).toBeInstanceOf(TestB)
})

API docs

PumpIt is written in TypeScript, auto generated API documentation is available.

License

This project is licensed under the MIT License - see the LICENSE file for details