Haywire

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Compile-time checked dependency injection for TypeScript: no decorators, no reflect-metadata, no global state.

Missing bindings, mismatched types and duplicate registrations are all TypeScript errors, so a container that compiles has everything it needs.

import { bind, createContainer, createModule, identifier, singletonScope } from 'haywire';

interface Logger {
    info(message: string): void;
}
const loggerId = identifier<Logger>();
const dbUrlId = identifier<string>().named('dbUrl');

class UserService {
    constructor(
        private readonly logger: Logger,
        private readonly dbUrl: string
    ) {}
}

const appModule = createModule(bind(loggerId).withFactory(() => console).scoped(singletonScope))
    .addBinding(bind(dbUrlId).withInstance('postgres://localhost/app'))
    .addBinding(bind(UserService).withDependencies([loggerId, dbUrlId]).withConstructorProvider());

const container = createContainer(appModule);

const userService = container.get(UserService);
         
const userService: UserService

Hover over any identifier in the examples on this site to see its inferred type. Every example is type-checked against Haywire's published types when the site is built.

Get started → · Why Haywire?

Features

• Wiring mistakes are type errors: A missing dependency, a duplicate binding, the wrong id passed to container.get(), or a nullable value injected into a non-nullable parameter all fail to build.
• Plain JavaScript: Constructor injection with no decorators, experimentalDecorators or reflect-metadata. Works with private fields, and in plain JavaScript too.
• Type-based ids, not strings: identifier<T>() tells two string dependencies, such as a database URL and password, apart at the type level.
• Real-world lifecycles: Singleton, request and transient scopes, opt-in async initialization, explicit circular dependencies, runtime values like an HTTP request supplied per call, and await using disposal of what the container created.
• Immutable and independent: Modules never mutate, and containers share no global registry, so tests can build their own and swap in fakes with a type-checked replaceBinding().

Compared to

• InversifyJS, TSyringe, TypeDI and NestJS's injector rely on decorators and string or token keys, and find missing bindings at runtime.
• Awilix avoids decorators, but resolves dependencies by name at runtime.

Haywire is the only one of these where a container that compiles is guaranteed to have every binding it needs.

Related

Packages

• haywire-launcher

  Run a Haywire-built entry script in one line, building the container only when the script runs.

Used in demos

• Read-through cache

  BentoCache on Valkey: a memory tier kept in sync, stale-while-revalidate, one load per key across instances, and sharding over several nodes with weighted rendezvous hashing.

• OpenAPI

  A notes API from spec to database: an OpenAPI 3.1 document built from Juniper schemas, genever types for a typed client and a Hono server that validates every request and response, and Drizzle on Postgres with a database per test.

• MCP server

  Making the notes API easy for AI agents that connect to services: tools shaped for tasks, an OAuth resource server with step-up scopes, and token exchange to call the API as the agent’s user.

• CLI for agents

  Making the notes API easy for AI agents with a shell: one short command per task, logging in once from the API’s URL, with tokens, refresh and errors handled inside.