depinj - A Dependency Injection linrary

A simple Dependency Injection library written in TypeScript compatible with vanilla JavaScript recommended for NodeJS.

Usage

Installation npm install --save depinj-js

Example

import { Builder, Injector, ScopeType } from 'depinj-js';

// Registering instances
const builder = new Builder().add(
    'FooService',
    () => ({ foo: 'bar' }),
    ScopeType.SingleInstance
);

const registry = builder.build();

// Retrieving instances
const injector = new Injector(registry);
const service = injector.getService('FooService');

// logs 'bar'
console.log(service.foo);

Example repo: depinj-express-example

Core Philosophy

Most JS written IoC libraries seem to be heavily opinianted and in my opinion violate the Open/Close principle. This is because the service that we are configuring requires annotations or other external syntax that binds the service concretization with the IoC engine.

This library intends on fixing this using a very simple principle. The configuration logic should be all concentrated in the Builder class.

Simplicity

This library tries to make the concept of Inversion of Control and Dependency

Principles

There are 3 components to the configuration of this library:

1. Configuration
2. Resolving
3. Scopes and Lifetimes

Configuration

builder.ts

Configuration should be only done once in an application's lifetime and should only happen in a centralized place. The purpose of this step is to create a dependency tree. This is a graph where all the services are linked with the services on which they depend.

The library supports a validation plugin that attempts at identifying possible configuration issues.

The builder instance is immutable, every time an add function is called a new instance is created. To get dependency tree (Registry) to add to an injector, call the build() method.

Resolving

injector.ts

Once the build() method is called, an Injector can be created. An Injector depends on a Registry (dependency tree) instance and a context (optional), the context is a generic object where the Injector will decorate the dependency context, this will be where the instances created from the same scope are stored.

Scopes and Lifetimes

An Injector is bound to a scope. However it can be chained by adding another scope. This will create a child Injector instance from another. All instances obtained by this child are only stored in the child's scope.

All instances are configured with one of 3 lifetime scopes. These are the configurations that allow for the Injector to decide if it's going to re-use an existing instance or creating a new one. For example, SingleInstances are re-used through the whole application lifetime, while Transient ones are re-used only during a specific scope. Depinj supports 3 lifetime scope types.

Since the Injector is bound to a context, whenever that context is disposed, its services need to be disposed, therefore the Injector exposes a public method, endScope which will call all the onScopeEnd callback for each service registered with this callback. This is an advanced use.

Integrations

There's a depinj-express integration package.