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Minimal and explicit dependency-injection & lifecycle container for stateful app components.

Inspired by Stuart Sierra's component framework for Clojure/ClojureScript.

Uses a declarative approach to define system components with a simple lifecycle API.


STABLE - used in production

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yarn add @thi.ng/system

ES module import:

<script type="module" src="https://cdn.skypack.dev/@thi.ng/system"></script>

Skypack documentation

For Node.js REPL:

const system = await import("@thi.ng/system");

Package sizes (brotli'd, pre-treeshake): ESM: 562 bytes


Usage examples

One project in this repo's /examples directory is using this package:

Screenshot Description Live demo Source
Declarative component-based system with central rstream-based pubsub event bus Demo Source


Generated API docs


Example system

import { defSystem, ILifecycle } from "@thi.ng/system";

// Step 1: Define the structure / components of your system

interface FooSys {
    db: DB;
    cache: Cache;
    logger: Logger;
    dummy: ILifecycle;

// Step 2: Provide component implementations
// Components can be classes or any object implementing the (fully optional)
// `ILifecycle` interface...

class Logger implements ILifecycle {

    info(msg: string) {
        console.log(`[info] ${msg}`);

    async start() {
        this.info("start logger");
        return true;

    async stop() {
        this.info("stop logger");
        return true;

// DB requires a logger & cache

class DB implements ILifecycle {

    constructor(protected logger: Logger, protected cache: Cache) {}

    async start() {
        this.logger.info("start db");
        return true;

    async stop() {
        this.logger.info("stop db");
        return true;

class Cache implements ILifecycle {

    constructor(protected logger: Logger) {}

    async start() {
        this.logger.info("start cache");
        return true;

    async stop() {
        this.logger.info("stop cache");
        return true;

// Step 3: Define system & component dependencies
// This will initialize all components in dependency order

// - All arg types and dependency IDs are inferred / type checked
// - `System` itself implements `ILifecycle`, so can be used to form
//   nested systems

const FOO = defSystem<FooSys>({
    db: {
        factory: async (deps) => new DB(deps.logger, deps.cache),
        deps: ["logger", "cache"],
    logger: { factory: async () => new Logger() },
    cache: {
        factory: async ({ logger }) => new Cache(logger),
        deps: ["logger"],
    dummy: {
        factory: async ({ logger }) => ({
            async start() {
                logger.info("start dummy");
                return true;
            async stop() {
                logger.info("stop dummy");
                return true;
        deps: ["logger"]

// Step 4: Asynchronously start all components in dependency order
await FOO.start();
// [info] start logger
// [info] start cache
// [info] start dummy
// [info] start db

// Step 5 (optional): Async shutdown all (in reverse order)
await FOO.stop();
// [info] stop db
// [info] stop dummy
// [info] stop cache
// [info] stop logger

// Alternatively, calls stop() & if successful followed by start()
await FOO.reset();

System visualization

For a System to initialize its components in the correct order, an internal dependency graph is constructed. This graph is not required any further after system initialization (see System.init()), though can be useful for debugging and documentation purposes.

For example, we can utilize the @thi.ng/dgraph-dot package to generate a Graphviz source file to visualize the dependencies between the system's components.

import { toDot } from "@thi.ng/dgraph-dot";

console.log(toDot(FOO.graph, { id: (node) => node }));
// digraph g {
// "db"[label="db"];
// "logger"[label="logger"];
// "cache"[label="cache"];
// "dummy"[label="dummy"];
// "db" -> "logger";
// "db" -> "cache";
// "cache" -> "logger";
// "dummy" -> "logger";
// }

Resulting visualization:

graphviz output


If this project contributes to an academic publication, please cite it as:

  title = "@thi.ng/system",
  author = "Karsten Schmidt and others",
  note = "https://thi.ng/system",
  year = 2020


© 2020 - 2024 Karsten Schmidt // Apache License 2.0

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