A simple IOC container for Typescript

Introduction

An IOC (Inversion of Control) container for Typescript.

The idea behind is to create a simple container that can be used to register and resolve dependencies working with classes & functions but without reflect metadata.

It is using simple Typescript code, so it can be used in any project without any dependency.

Works also in NextJS middleware and node+edge runtimes.

Installation

npm i @evyweb/ioctopus

How to use

To use the container, you need to create a container and bind your dependencies. To do so you need to create an id for each dependency you want to register.

This id that we call an "injection token" can be a string or a symbol. (Please note that you have to be consistent and use always strings for binding and resolving dependencies or always symbols, you can't mix them).

Then you can bind the dependency to a value, a function, a class, a factory, a higher order function, or a curried function.

Using symbols as injection tokens

(You can skip "step a" if you prefer to use strings as injection tokens).

a) Create a symbol for each dependency you want to register. It will be used to identify the dependency.

export const DI: InjectionTokens = {
    DEP1: Symbol('DEP1'),
    DEP2: Symbol('DEP2'),
    LOGGER: Symbol('LOGGER'),
    MY_SERVICE: Symbol('MY_SERVICE'),
    MY_USE_CASE: Symbol('MY_USE_CASE'),
    SIMPLE_FUNCTION: Symbol('SIMPLE_FUNCTION'),
    CLASS_WITH_DEPENDENCIES: Symbol('CLASS_WITH_DEPENDENCIES'),
    CLASS_WITHOUT_DEPENDENCIES: Symbol('CLASS_WITHOUT_DEPENDENCIES'),
    HIGHER_ORDER_FUNCTION_WITH_DEPENDENCIES: Symbol('HIGHER_ORDER_FUNCTION_WITH_DEPENDENCIES'),
    HIGHER_ORDER_FUNCTION_WITHOUT_DEPENDENCIES: Symbol('HIGHER_ORDER_FUNCTION_WITHOUT_DEPENDENCIES')
} ;

b) Then create your container.

import { DI } from './di';

const container: Container = createContainer();

Register the dependencies

Primitives

You can register primitives

container.bind(DI.DEP1).toValue('dependency1');
container.bind(DI.DEP2).toValue(42);

// or using strings
container.bind('DEP1').toValue('dependency1');
container.bind('DEP2').toValue(42);

Functions

• You can register functions without dependencies

const sayHelloWorld = () => console.log('Hello World');

container.bind(DI.SIMPLE_FUNCTION).toFunction(sayHelloWorld);

// or using strings
container.bind('SIMPLE_FUNCTION').toFunction(sayHelloWorld);

Currying

• You can register functions with dependencies using currying (1 level of currying)

const myFunction = (dep1: string, dep2: number) => (name: string) => console.log(`${dep1} ${dep2} ${name}`);

container.bind(DI.CURRIED_FUNCTION_WITH_DEPENDENCIES)
    .toCurry(myFunction, [DI.DEP1, DI.DEP2]);

// or using strings
container.bind('CURRIED_FUNCTION_WITH_DEPENDENCIES')
    .toCurry(myFunction, ['DEP1', 'DEP2']);

• You can also use a dependency object

interface Dependencies {
    dep1: string,
    dep2: number
}

const myFunction = (dependencies: Dependencies) => (name: string) => console.log(`${dependencies.dep1} ${dependencies.dep2} ${name}`);

// The dependencies will be listed in an object in the second parameter
container.bind(DI.CURRIED_FUNCTION_WITH_DEPENDENCIES)
    .toCurry(myFunction, {dep1: DI.DEP1, dep2: DI.DEP2});

// or using strings
container.bind('CURRIED_FUNCTION_WITH_DEPENDENCIES')
    .toCurry(myFunction, {dep1: 'DEP1', dep2: 'DEP2'});

Higher order functions

You can also register functions with dependencies by using higher order functions

const MyServiceWithDependencies = (dep1: string, dep2: number): MyServiceWithDependenciesInterface => {
    return {
        runTask: () => {
            // Do something with dep1 and dep2
        }
    };
};

// The dependencies will be listed in an array in the second parameter
container.bind(DI.HIGHER_ORDER_FUNCTION_WITH_DEPENDENCIES)
    .toHigherOrderFunction(MyServiceWithDependencies, [DI.DEP1, DI.DEP2]);

// or using strings
container.bind('HIGHER_ORDER_FUNCTION_WITH_DEPENDENCIES')
    .toHigherOrderFunction(MyServiceWithDependencies, ['DEP1', 'DEP2']);

But if you prefer, you can also use a dependency object

interface Dependencies {
    dep1: string,
    dep2: number
}

const MyService = (dependencies: Dependencies): MyServiceInterface => {
    return {
        runTask: () => {
            // Do something with dependencies.dep1 and dependencies.dep2
        }
    };
};

// The dependencies will be listed in an object in the second parameter
container.bind(DI.HIGHER_ORDER_FUNCTION_WITH_DEPENDENCIES)
    .toHigherOrderFunction(MyService, {dep1: DI.DEP1, dep2: DI.DEP2});

// or using strings
container.bind('HIGHER_ORDER_FUNCTION_WITH_DEPENDENCIES')
    .toHigherOrderFunction(MyService, {dep1: 'DEP1', dep2: 'DEP2'});

Factories

For more complex cases, you can register factories.

container.bind(DI.MY_USE_CASE).toFactory(() => {
    // Do something before creating the instance
     
    // Then return the instance
    return MyUseCase({
        myService: container.get<MyService>(DI.MY_SERVICE)
    });
});

// or using strings
container.bind('MY_USE_CASE').toFactory(() => {
    // Do something before creating the instance
     
    // Then return the instance
    return MyUseCase({
        myService: container.get<MyService>('MY_SERVICE')
    });
});

Classes

You can register classes, the dependencies of the class will be resolved and injected in the constructor

class MyServiceClass implements MyServiceClassInterface {
    constructor(
        private readonly dep1: string,
        private readonly dep2: number,
    ) {}

    runTask(): string {
        return `Executing with dep1: ${this.dep1} and dep2: ${this.dep2}`;
    }
}

container.bind(DI.CLASS_WITH_DEPENDENCIES).toClass(MyServiceClass, [DI.DEP1, DI.DEP2]);

// or using strings
container.bind('CLASS_WITH_DEPENDENCIES').toClass(MyServiceClass, ['DEP1', 'DEP2']);

But if you prefer, you can also use a dependency object:

interface Dependencies {
    dep1: string,
    dep2: number
}

class MyServiceClass implements MyServiceClassInterface {
    constructor(private readonly dependencies: Dependencies) {}

    runTask(): string {
        return `Executing with dep1: ${this.dependencies.dep1} and dep2: ${this.dependencies.dep2}`;
    }
}

container.bind(DI.CLASS_WITH_DEPENDENCIES).toClass(MyServiceClass, {dep1: DI.DEP1, dep2: DI.DEP2});

// or using strings
container.bind('CLASS_WITH_DEPENDENCIES').toClass(MyServiceClass, {dep1: 'DEP1', dep2: 'DEP2'});

• You can register classes without dependencies:

class MyServiceClassWithoutDependencies implements MyServiceClassInterface {
    runTask(): string {
        return `Executing without dependencies`;
    }
}

container.bind(DI.CLASS_WITHOUT_DEPENDENCIES).toClass(MyServiceClassWithoutDependencies);
    
// or using strings
container.bind('CLASS_WITHOUT_DEPENDENCIES').toClass(MyServiceClassWithoutDependencies);

Resolve the dependencies

You can now resolve the dependencies using the get method of the container.

import { DI } from './di';

// Primitive
const dep1 = container.get<string>(DI.DEP1); // 'dependency1'
const dep2 = container.get<number>(DI.DEP2); // 42
// or using strings
const dep1 = container.get<string>('DEP1'); // 'dependency1'
const dep2 = container.get<number>('DEP2'); // 42

// Higher order function and class
const myUseCase = container.get<MyUseCaseInterface>(DI.MY_USE_CASE);
// or using strings
const myUseCase = container.get<MyUseCaseInterface>('MY_USE_CASE');
myUseCase.execute();
    
// Simple function
const simpleFunction = container.get<SimpleFunctionType>(DI.SIMPLE_FUNCTION);
// or using strings
const simpleFunction = container.get<SimpleFunctionType>('SIMPLE_FUNCTION');
simpleFunction('Hello World');

// Curried function
const callMe = container.get<CurriedFunction>(DI.CURRIED_FUNCTION_WITH_DEPENDENCIES);
// or using strings
const callMe = container.get<CurriedFunction>('CURRIED_FUNCTION_WITH_DEPENDENCIES');
callMe('John Doe');

Modules

You can also use modules to organize your dependencies.

Loading modules

Modules can then be loaded in your container. By default, when you create a container, it is using a default module under the hood.

const module1 = createModule();
module1.bind(DI.DEP1).toValue('dependency1');

const module2 = createModule();
module2.bind(DI.DEP2).toValue(42);

const module3 = createModule();
module3.bind(DI.MY_SERVICE).toHigherOrderFunction(MyService, {dep1: DI.DEP1, dep2: DI.DEP2});

const container = createContainer();
container.load(Symbol('module1'), module1);
container.load(Symbol('module2'), module2);
container.load(Symbol('module3'), module3);

const myService = container.get<MyServiceInterface>(DI.MY_SERVICE);

The dependencies do not need to be registered in the same module as the one that is using them. Note that the module name used as a key can be a symbol or a string.

Modules override

You can also override dependencies of a module. The dependencies of the module will be overridden by the dependencies of the last loaded module.

const module1 = createModule();
module1.bind(DI.DEP1).toValue('OLD dependency1');
module1.bind(DI.MY_SERVICE).toFunction(sayHelloWorld);

const module2 = createModule();
module2.bind(DI.DEP1).toValue('NEW dependency1');

const module3 = createModule();
module3.bind(DI.MY_SERVICE).toHigherOrderFunction(MyService, {dep1: DI.DEP1, dep2: DI.DEP2});

const container = createContainer();
container.bind(DI.DEP2).toValue(42); // Default module
container.load(Symbol('module1'), module1);
container.load(Symbol('module2'), module2);
container.load(Symbol('module3'), module3);

// The dependency DI.MY_SERVICE will be resolved with the higher order function and dep1 will be 'NEW dependency1'
const myService = container.get<MyServiceInterface>(DI.MY_SERVICE);

Unload modules

You can also unload a module from the container. The dependencies of the module will be removed from the container. Already cached instances will be removed to keep consistency and avoid potential errors.

const module1 = createModule();
module1.bind(DI.DEP1).toValue('dependency1');

const container = createContainer();
container.load(Symbol('module1'), module1);

container.unload(Symbol('module1'));

// Will throw an error as the dependency is not registered anymore
const myService = container.get<string>(DI.DEP1); 

Using scopes

Singleton scope (default)

In singleton scope, the container returns the same instance every time a dependency is resolved.

container.bind(DI.MY_SERVICE).toClass(MyServiceClass, [DI.DEP1, DI.DEP2]);
// or
container.bind(DI.MY_SERVICE).toClass(MyServiceClass, [DI.DEP1, DI.DEP2], 'singleton');

const instance1 = container.get<MyServiceClassInterface>(DI.MY_SERVICE);
const instance2 = container.get<MyServiceClassInterface>(DI.MY_SERVICE);

console.log(instance1 === instance2); // true

Transient scope

In transient scope, the container returns a new instance every time the dependency is resolved.

container.bind(DI.MY_SERVICE).toClass(MyServiceClass, [DI.DEP1, DI.DEP2], 'transient');

const instance1 = container.get<MyServiceClassInterface>(DI.MY_SERVICE);
const instance2 = container.get<MyServiceClassInterface>(DI.MY_SERVICE);

console.log(instance1 === instance2); // false

Scoped Scope

In scoped scope, the container returns the same instance within a scope. Different scopes will have different instances.

To use the scoped scope, you need to create a scope using runInScope.

container.bind(DI.MY_SERVICE).toClass(MyServiceClass, [DI.DEP1, DI.DEP2], 'scoped');
const instance1 = undefined;
const instance2 = undefined;

container.runInScope(() => {
    instance1 = container.get<MyServiceClassInterface>(DI.MY_SERVICE);
    instance2 = container.get<MyServiceClassInterface>(DI.MY_SERVICE);

    console.log(instance1 === instance2); // true
});

container.runInScope(() => {
    const instance3 = container.get<MyServiceClassInterface>(DI.MY_SERVICE);

    console.log(instance3 === instance1); // false
});

Note: If you try to resolve a scoped dependency outside a scope, an error will be thrown.

Circular dependencies

IOctopus can detect circular dependencies. An error will be thrown if a circular dependency is detected.

const container = createContainer();

const A_TOKEN = Symbol('A');
const B_TOKEN = Symbol('B');

class A {
    constructor(public b: B) {}
}

class B {
    constructor(public a: A) {}
}

container.bind(A_TOKEN).toClass(A, [B_TOKEN]);
container.bind(B_TOKEN).toClass(B, [A_TOKEN]);

container.get(A_TOKEN); // Will throw: "Circular dependency detected: Symbol(A) -> Symbol(B) -> Symbol(A)"

This way you can avoid infinite loops and stack overflow errors.