Injektion

Decorator-less dependency injection for JavaScript and TypeScript.

NOTE: This project is in early development, so expect bugs and missing features. Any help would be appreciated :)

Summary

• Why and how?
• Setup
• Usage
• API
  • Autoloading dependencies
  • Binding a dependency
  • Binding a custom name to a dependency
  • Binding a dependency as a singleton
  • Binding a dependency to a given instance
  • Binding a dependency with instructions on how to instantiate it
  • Getting a dependency from the container and recursively resolving its dependencies
  • Checking if a dependency exists in the container
• Development
  • Testing
  • Building

Why and how?

Long story, expand if you want to know more

I've tried several dependency injection frameworks for JavaScript and TypeScript. There are two main things I didn't like about them:

1. Decorators
2. Too much manual configuration

So I've started thinking about how a new dependency injection framework could be better.

First of all, I need to somehow get information about a specific class, like its name and constructor parameters. It turns out that JavaScript doesn't have a built-in Reflection API for that kind of task. So that's why they use reflect-metadata.

So I've created my own reflection package: reflection-function. Now I can get all those information from a function and a class.

But there's still a problem here: JavaScript doesn't have types. Even TypeScript doesn't have types at runtime or after the code has been compiled. How am I gonna know which dependency I have to inject if there's no information about types?

Well, the only thing that I have left is the parameter name. So that's what I'm going to use. Dependency injections are made based on the parameter name. For example, if you have a class named UserService and you need to inject it in another class constructor, you would name the parameter userService, or maybe user_service (the letter case is up to you).

Ok, now we have dependency injection without decorators. But what about "too much manual configuration"?

That's simple. I wrote a class that goes through all your project files and dynamically imports them (with import()). It works with default and named exports and it only imports classes. Those imports are stored in the dependency container and are available to use with zero configuration.

Of course, that works only for concrete classes. As in Laravel's service container, if your class depends on interfaces, you need to manually bind the interface to the concrete class. Well, while TypeScript does have interfaces, JavaScript doesn't, so in the end interfaces doesn't even exist at all, so you just manually bind a name, like UserRepository to a real object, like SequelizeUserRepository.

Setup

Install the package with:

npm install injektion

Create a file somewhere in your project to store your manual bindings, like for example a ./src/config/dependencies.ts with this content:

import { Container } from 'injektion';
import { LogParser } from './app/Utils'
import { SequelizeUserRepository } from './app/Repositories/Implementation';

export default () => {
  Container.singleton(LogParser);
  Container.namedBind('UserRepository', SequelizeUserRepository);
};

Somewhere where your application starts, run the default export of the file you just created (to bind the dependencies) and the autoload method from the container to automatically load the dependencies based on the base path you provided:

import { Container } from 'injektion';
import bindDependencies from './config/dependencies.ts';

// ...

bindDependencies();
await Container.autoload('./src/app');

Usage

To start resolving the dependencies, an entry point is needed. For example, if you have the dependency structure AuthController <- AuthService <- UserRepository, you would call the get method from the container, requesting the AuthController, and each dependency is recursively resolved:

import { Container } from 'injektion';

// ...

const authController = <AuthController>Container.get('AuthController');

Ensure that all of your constructor parameters have the same name as the class you want to inject. For example, if you want to inject a class named AuthService, name the parameter authService or in any case you want, like auth_service. The case is not important, the name itself is.

Check the API section below for more info.

API

Autoloading dependencies

Most of your dependencies can be autoloaded by Injektion. To do that, just call the autoload method from the container passing a base directory. Injektion will recursively scan for dependencies and bind them automatically in the container:

Container.autoload(baseDirectory: string, replace = false): Promise<void>;

// Example: without replacing binded dependencies
await Container.autoload('./src/app');

// Example: replacing binded dependencies
await Container.autoload('./src/app', true);

By default, the autoload method will not replace binded dependencies. This prevents your manual bindings to get overridden. However, if you still want to replace automatically, just pass true as the second parameter.

Binding a dependency

You can also manually bind a dependency in the container by providing a reference to the class:

Container.bind(reference: Function): void;

// Example
import { AuthController } from './app/Controllers';

Container.bind(AuthController)

Binding a custom name to a dependency

Because JavaScript does not have interfaces, we provide a namedBind method that allows you to simulate this kind of behavior. Take the example below, whenever Injektion finds a UserRepository dependency, it will auto inject SequelizeUserRepository. You can now swap implementations with just one line of code:

Container.namedBind(name: string, reference: Function): void;

// Example
import { SequelizeUserRepository } from './app/Repositories/Implementation';

Container.namedBind('UserRepository', SequelizeUserRepository)

Binding a dependency as a singleton

The singleton method binds a dependency that should only be instantiated one time. Once a singleton is resolved, the same instance will be returned on subsequent calls:

Container.singleton(reference: Function): void;

// Example
import { AuthService } from './app/Services';

Container.singleton(AuthService);

Binding a dependency to a given instance

You can also bind an existing instance into the container using the instance method:

Container.instance(reference: Function, instance: any): void;

// Example
import { BlogCrawler } from './app/BlogCrawler';

const crawler = new BlogCrawler('https://some.blog/');

Container.instance(BlogCrawler, crawler);

Binding a dependency with instructions on how to instantiate it

The instructions method binds a dependency with manual instructions on how to instantiate it. The method accepts a callback that returns an instance of the class. You can access the Container class through the first parameter of the callback:

Container.instructions(name: string, instructions: Instructions): void;

// Example

import { SpreadsheetParser } from './app/SpreadsheetParser';

Container.instructions('SpreadsheetParser', (container) => (
  new SpreadsheetParser(
    container.get('FileReader'),
    'xlsx',
  )
))

Getting a dependency from the container and recursively resolving its dependencies

You can use the get method to get a dependency instance from the container, just pass the dependency name you wish to resolve:

Container.get<T>(name: string): T;

// Example
import { MailFacade } from './app/Facades';

const mailFacade = <MailFacade>Container.get('MailFacade');

If you are using TypeScript, you can also provide a type argument to light up IntelliSense.

Checking if a dependency exists in the container

Last but not least, you can also check if a given dependency exists in the container by providing its name:

Container.has(name: string): boolean;

// Example
const exists = Container.has('ActivationService');

Development

Install the dependencies:

npm install

All source codes are located in the src directory.

Testing

To run the tests, run in your terminal:

npm run test

To check the code coverage, run in your terminal:

npm run coverage

And then open in the browser the file coverage/lcov-report/index.html.

Building

To build the package, run:

npm run build

The generated JavaScript code is located in the dist directory.