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

Module

Module provides a list of providers and can connect other modules

Features

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

Usage

Installation

npm

npm install @tinkoff/dippy

Yarn

yarn add @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([]);

initContainer({ modules, providers })

initContainer method is a wrapper over createContainer method and used to create an instance of the container and walk over all modules.

Example:

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

const di = initContainer({
  modules: [],
  providers: [],
});

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:

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

// with special `optional` utility
// `string` | `null` if not found
const foo1 = container.get(optional(FOO_TOKEN));

// without `optional` utility
// `string` | `null` if not found
const foo2 = 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);

Multi optional token:

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

// `{ key: string }[]` | empty `[]` if not found
const list = container.get(optional(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' },
});

Module

Module - Decorator for configuring and creating a module.

Read more about modules

@Module({ providers, deps, imports })(class)

• providers - Providers, which will be added to the root DI container and become available in other modules
• deps - List of dependencies from the DI container, necessary to initialize the module
• imports - A list of modules from which providers will be obtained and added to the DI. Allows you to create modules that combine many other modules

Usage

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

@Module({
  providers: [
    provide({
      provide: 'token',
      useValue: 'value-in-token',
    }),
  ],
  deps: {
    logger: 'logger',
  },
  imports: [ModuleLogger],
})
class ModulePubSub {
  constructor({ logger }) {
    logger.info('Module created');
  }
}

declareModule

declareModule - factory for configuring and creating a module.

Read more about modules

declareModule({ name, providers, imports, extend })

• name - Unique module name
• providers - Providers, which will be added to the root DI container and become available in other modules
• imports - A list of modules from which providers will be obtained and added to the DI. Allows you to create modules that combine many other modules
• extend - A list of module configuration methods

Usage

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

const ModulePubSub = declareModule({
  name: 'PubSub',
  imports: [ModuleLogger],
  providers: [
    provide({
      provide: 'token',
      useValue: 'value-in-token',
    }),
  ],
  extend: {
    forRoot(tokenValue: string) {
      return [
        provide({
          provide: 'token',
          useValue: tokenValue,
        }),
      ];
    },
  },
});

// use ModulePubSub or ModulePubSub.forRoot('new value')