ditox package

Dependency injection for modular web applications

Please see the documentation at ditox.js.org

Installation

You can use the following command to install this package:

npm install --save ditox

The package can be used as UMD module. Use jsdelivr.com CDN site to load ditox:

<script src="//cdn.jsdelivr.net/npm/ditox/dist/umd/index.js" />
<script>
  const container = Ditox.createContainer();
</script>

General description

DI pattern in general allows to declare and construct a code graph of an application. It can be described by following phases:

1. Code declaration phase:

• Defining public API and types of business layer
• Creation of injection tokens
• Declaring DI modules

2. Binding phase:

• Creation of a container
• Binding values, factories and modules to the container

3. Runtime phase:

• Running the code
• Values are constructed by registered factories

Diagram:

Usage Example

import {createContainer, injectable, optional, token} from 'ditox';

// This is app code, some factory functions and classes:
function createStorage(config) {}

function createLogger(config) {}

class UserService {
  constructor(storage, logger) {}
}

// Define tokens for injections.
const STORAGE_TOKEN = token < UserService > 'Token description for debugging';
const LOGGER_TOKEN = token();
const USER_SERVICE_TOKEN = token();

// Token can be optional with a default value.
const STORAGE_CONFIG_TOKEN = optional(token(), {name: 'default storage'});

// Create the container.
const container = createContainer();

// Provide a value to the container.
container.bindValue(STORAGE_CONFIG_TOKEN, {name: 'custom storage'});

// Dynamic values are provided by factories.

// A factory can be decorated with `injectable()` to resolve its arguments.
// By default, a factory has `singleton` lifetime.
container.bindFactory(
  STORAGE_TOKEN,
  injectable(createStorage, STORAGE_CONFIG_TOKEN),
);

// A factory can have `transient` lifetime to create a value on each resolving.
container.bindFactory(LOGGER_TOKEN, createLogger, {scope: 'transient'});

// A class can be injected by `injectableClass()` which calls its constructor
// with injected dependencies as arguments.
container.bindFactory(
  USER_SERVICE_TOKEN,
  injectable(
    (storage, logger) => new UserService(storage, logger),
    STORAGE_TOKEN,
    // A token can be made optional to resolve with a default value
    // when it is not found during resolving.
    optional(LOGGER_TOKEN),
  ),
  {
    // `scoped` and `singleton` scopes can have `onRemoved` callback.
    // It is called when a token is removed from the container.
    scope: 'scoped',
    onRemoved: (userService) => userService.destroy(),
  },
);

// Get a value from the container, it returns `undefined` in case a value is not found.
const logger = container.get(LOGGER_TOKEN);

// Resolve a value, it throws `ResolverError` in case a value is not found.
const userService = container.resolve(USER_SERVICE_TOKEN);

// Remove a value from the container.
container.remove(LOGGER_TOKEN);

// Clean up the container.
container.removeAll();

Container Hierarchy

Ditox.js supports "parent-child" hierarchy. If the child container cannot to resolve a token, it asks the parent container to resolve it:

import {creatContainer, token} from 'ditox';

const V1_TOKEN = token();
const V2_TOKEN = token();

const parent = createContainer();
parent.bindValue(V1_TOKEN, 10);
parent.bindValue(V2_TOKEN, 20);

const container = createContainer(parent);
container.bindValue(V2_TOKEN, 21);

container.resolve(V1_TOKEN); // 10
container.resolve(V2_TOKEN); // 21

Factory Lifetimes

Ditox.js supports managing the lifetime of values which are produced by factories. There are the following types:

• singleton - This is the default. The value is created and cached by the most distant parent container which owns the factory function.
• scoped - The value is created and cached by the nearest container which owns the factory function.
• transient - The value is created every time it is resolved.

singleton

This is the default scope. "Singleton" allows to cache a produced value by a most distant parent container which registered the factory function:

import {creatContainer, token} from 'ditox';

const TAG_TOKEN = token();
const LOGGER_TOKEN = token();

const createLogger = (tag) => (message) => console.log(`[${tag}] ${message}`);

const parent = createContainer();
parent.bindValue(TAG_TOKEN, 'parent');
parent.bindFactory(LOGGER_TOKEN, injectable(createLogger, TAG_TOKEN), {
  scope: 'singleton',
});

const container1 = createContainer(parent);
container1.bindValue(TAG_TOKEN, 'container1');

const container2 = createContainer(parent);
container2.bindValue(TAG_TOKEN, 'container2');

parent.resolve(LOGGER_TOKEN)('xyz'); // [parent] xyz
container1.resolve(LOGGER_TOKEN)('foo'); // [parent] foo
container2.resolve(LOGGER_TOKEN)('bar'); // [parent] bar

scoped

"Scoped" lifetime allows to have sub-containers with own instances of some services which can be disposed. For example, a context during HTTP request handling, or other unit of work:

import {creatContainer, token} from 'ditox';

const TAG_TOKEN = token();
const LOGGER_TOKEN = token();

const createLogger = (tag) => (message) => console.log(`[${tag}] ${message}`);

const parent = createContainer();
// `scoped` is default scope and can be omitted.
parent.bindFactory(LOGGER_TOKEN, injectable(createLogger, TAG_TOKEN), {
  scope: 'scoped',
});

const container1 = createContainer(parent);
container1.bindValue(TAG_TOKEN, 'container1');

const container2 = createContainer(parent);
container2.bindValue(TAG_TOKEN, 'container2');

parent.resolve(LOGGER_TOKEN)('xyz'); // throws ResolverError, the parent does not have TAG value.
container1.resolve(LOGGER_TOKEN)('foo'); // [container1] foo
container2.resolve(LOGGER_TOKEN)('bar'); // [container2] bar

// Dispose a container.
container1.removeAll();

transient

"Transient" makes to a produce values by the factory for each resolving:

import {createContainer, token} from 'ditox';

const TAG_TOKEN = token();
const LOGGER_TOKEN = token();

const createLogger = (tag) => (message) => console.log(`[${tag}] ${message}`);

const parent = createContainer();
parent.bindValue(TAG_TOKEN, 'parent');
parent.bindFactory(LOGGER_TOKEN, injectable(createLogger, TAG_TOKEN), {
  scope: 'transient',
});

const container1 = createContainer(parent);
container1.bindValue(TAG_TOKEN, 'container1');

const container2 = createContainer(parent);
container2.bindValue(TAG_TOKEN, 'container2');

parent.resolve(LOGGER_TOKEN)('xyz'); // [parent] xyz
container1.resolve(LOGGER_TOKEN)('foo'); // [container1] foo
container2.resolve(LOGGER_TOKEN)('bar'); // [container2] bar

parent.bindValue(TAG_TOKEN, 'parent-rebind');
parent.resolve(LOGGER_TOKEN)('xyz'); // [parent-rebind] xyz

Dependency Modules

Dependencies can be organized as modules in declarative way with ModuleDeclaration. It is useful for providing pieces of functionality from libraries to an app which depends on them.

import {Module, ModuleDeclaration, token} from 'ditox';
import {TRANSPORT_TOKEN} from './transport';

export type Logger = {log: (message: string) => void};
export const LOGGER_TOKEN = token<Logger>();

type LoggerModule = Module<{logger: Logger}>;

const LOGGER_MODULE_TOKEN = token<LoggerModule>();

const LOGGER_MODULE: ModuleDeclaration<LoggerModule> = {
  // An optional explicit token for a module itself
  token: LOGGER_MODULE_TOKEN,

  factory: (container) => {
    const transport = container.resolve(TRANSPORT_TOKEN).open();
    return {
      logger: {log: (message) => transport.write(message)},
      destroy: () => transport.close(),
    };
  },
  exports: {
    logger: LOGGER_TOKEN,
  },
};

Later such module declarations can be bound to a container:

const container = createContainer();

// bind a single module
bindModule(container, LOGGER_MODULE);

// or bind multiple depenendency modules
bindModules(container, [DATABASE_MODULE, CONFIG_MODULE, API_MODULE]);

Utility functions for module declarations:

• declareModule() – declare a module as ModuleDeclaration however token field can be optional for anonymous modules.
• declareModuleBindings() – declares an anonymous module with imports. This module binds the provided ones to a container.

Example for these functions:

const LOGGER_MODULE = declareModule<LoggerModule>({
  factory: createLoggerModule,
  exports: {
    logger: LOGGER_TOKEN,
  },
});

const APP_MODULE = declareModuleBinding([LOGGER_MODULE, DATABASE_MODULE]);

This project is licensed under the MIT license.