@tinkoff/dippy

@tinkoff/dippy

Inversion of Control pattern implementation

Explanation

dippy brings Dependency Injection system to your applications. Dependency Injection provides a powerful way to make applications modular, flexible and extensible.

Dependency

Dependency is a peace of code that has a specific purpose - primitive value, object, class instance.

Container

Container contains information about dependencies, connections between them, and already created instances of dependencies

Token

Token represents a dependency by unique key and typed interface

Provider

Provider provides dependency implementation by token, and indicates connections between other dependencies

Features

• Dynamic initialization
• Replacing implementations
• Multi tokens
• Child containers
• Lightweight
• Does not use reflect-metadata and decorators
• Circular dependency safe
• Easy to debug

Usage

Installation

npm install @tinkoff/dippy

Quick start

import {
  createContainer,
  createToken,
  provide,
} from '@tinkoff/dippy';

const COUNTER = createToken<{ value: number }>('counter');
const MULTIPLIER = createToken<{ value: number }>('multiplier');

const providers = [
  provide({
    provide: COUNTER,
    useValue: { value: 2 },
  }),
  provide({
    provide: MULTIPLIER,
    useFactory(deps) {
      return {
        value: deps.counter.value * 2,
      };
    },
    deps: {
      counter: COUNTER,
    },
  }),
];

const container = createContainer(providers);

console.log(container.get(MULTIPLIER)); // 4

API

Token

createToken(name, options)

createToken method creates token - both key and interface for dependency. name argument - string key, name of the dependency. Optional options argument - specific token parameters.

Basic example:

const FOO_TOKEN = createToken<{ key: string }>('foo');

Multi token:

const FOO_LIST_TOKEN = createToken<{ key: string }>('foo list', { multi: true });

typeof token

createToken returns type of the dependency, e.g.:

const FOO_TOKEN = createToken<{ key: string }>('foo');

// { key: string }
type InferedFooType = typeof FOO_TOKEN;

Container

createContainer(providers)

createContainer method is used to create an instance of the container. Optional provider argument - list of default providers.

Example:

import { createContainer } from '@tinkoff/dippy';

const container = createContainer([]);

container.get(token)

get method returns resolved dependency instance or resolves this token with his dependencies.

Basic example:

// string
const foo = container.get(FOO_TOKEN);

Optional dependency:

// string | null
const foo = container.get({ token: FOO_TOKEN, optional: true });

Multi token:

const LIST_TOKEN = createToken<{ key: string }>('list', { multi: true });

// { key: string }[]
const list = container.get(LIST_TOKEN);

container.register(provider)

register method saves provider for token, and can overwrite previous registered provider for the same token.

Value provider:

container.register({
  provide: FOO_TOKEN,
  useValue: { key: 'a' },
});

Multi provider:

const LIST_TOKEN = createToken<{ key: string }>('list', { multi: true });

container.register({
  provide: LIST_TOKEN,
  multi: true,
  useValue: { key: 'a' },
});

container.register({
  provide: LIST_TOKEN,
  multi: true,
  useValue: [{ key: 'b' }, { key: 'c' }],
});

console.log(container.get(LIST_TOKEN)); // [{ key: 'a' }, { key: 'b' }, { key: 'c' }]

Factory provider:

container.register({
  provide: BAR_TOKEN,
  useFactory(deps) {
    return `${deps.foo} Bar`;
  },
  deps: {
    foo: FOO_TOKEN,
  },
})

Class provider:

class Bar {
  constructor(private foo: string) {}
}

container.register({
  provide: BAR_TOKEN,
  useClass: Bar,
  deps: {
    foo: FOO_TOKEN,
  },
})

Child container

It is enough to have only one DI container for client SPA applications. But for server-side applications (SSR or API, no difference), you may need to create unique container for every request into the application. For this reason, dippy provides ability to "fork" root DI container, which allows us to reuse providers from root container, and even providers implementations, if they were registered in Scope.SINGLETON.

Quick start

import express from 'express';
import type { Request, Response } from 'express';
import {
  createContainer,
  createToken,
  provide,
  Scope,
} from '@tinkoff/dippy';

const app = express();
const rootDi = createContainer();

const LOGGER = createToken<Console>('logger');
const REQUEST = createToken<Request>('request');
const RESPONSE = createToken<Response>('response');

rootDi.register({
  provide: LOGGER,
  scope: Scope.SINGLETON,
  useFactory() {
    // will be executed only once
    return console;
  },
})

app.get('/', (req, res) => {
  const childDI = createChildContainer(rootDi);
  // the same logger for every request
  const logger = childDI.get(LOGGER);

  // unique req object for request
  childDI.register({
    provide: REQUEST,
    useValue: req,
  });
  // unique res object for request
  childDI.register({
    provide: RESPONSE,
    useValue: res,
  });

  res.send('Hello World!');
});

Scope

Enum Scope has two values - REQUEST and SINGLETON. Default value for every provider is REQUEST. If provider from parent DI has scope REQUEST, every child DI will resolve own implementation of this provider. If provider has scope SINGLETON, every child DI will reuse the same resolved implementation of this provider from parent DI.

Basic example:

container.register({
  provide: FOO_TOKEN,
  useValue: { foo: 'bar' },
});

Singleton example:

container.register({
  provide: FOO_TOKEN,
  scope: Scope.SINGLETON,
  useValue: { foo: 'bar' },
});