What is a service?

A service holds state or logic that needs to stay consistent across the whole app, independent of any single component's or view's lifecycle. Every service extends the abstract Service<T> base class, which is a singleton — Nutin guarantees at most one instance of each service class exists.

export class ExampleService extends Service<ExampleService> {}
export const exampleService = ExampleService.getInstance();

Calling new ExampleService() directly throws — getInstance() is the only valid construction path, and the "consistency" a service provides comes precisely from that guarantee: every consumer that imports the exported singleton const is reading and writing the same instance. There's no dependency-injection container — a component, view, or another service just imports the const and calls its methods.

See How do I create a service? and How do I use a service?.

Every service method is auto-bound to its instance at construction, so methods can be destructured or passed around as bare callbacks without losing this.

Cleanup

A service has two independent teardown paths — dispose() (runs registerCleanup()-queued callbacks, wired automatically to window.beforeunload) and Service.destroy()/destroyAll() (awaits the onDestroy() hook). They cover different kinds of teardown and aren't interchangeable. See How do I register service cleanup?.

Nutin services are services too

Nutin's own cross-cutting pieces are built the same way application services are. As an example, AppEventBus (the app event bus — see What are events in Nutin?) and Router (see How do I register a route?) are both Service singletons under the hood.