Apa iku EventEmitter lan carane digunakake?

Question

Accepted Answer

**EventEmitter** minangka kelas Node inti sing ngetrapake pola **publish/subscribe**: obyek nglumpukake event sing dinami, lan listener sing didaftar kanggo event-event kuwi bakal mlaku nalika maeya. Akeh API Node dhewe (streams, HTTP servers, process) dibangun ing iku.

## Panganggone dhasar

```js
import { EventEmitter } from "events";

const emitter = new EventEmitter();

// SUBSCRIBE: register a listener for an event
emitter.on("order", (order) => {
  console.log(`Processing order ${order.id}`);
});

// PUBLISH: emit the event (with optional data)
emitter.emit("order", { id: 123 }); // → "Processing order 123"
```

Pola: `on(event, listener)` nglumukake; `emit(event, ...args)` ngetrigger kabeh listener kanggo event kuwi kanthi sinkron, menehi argumen-argumen.

## Ngluwihi EventEmitter kanggo kelas-kelas dhuwurmu

```js
class OrderService extends EventEmitter {
  placeOrder(order) {
    // ...save the order...
    this.emit("order:created", order);  // notify anyone interested
  }
}

const service = new OrderService();
service.on("order:created", (o) => sendEmail(o));   // decoupled listeners
service.on("order:created", (o) => updateAnalytics(o));
service.placeOrder({ id: 1 }); // both listeners run
```

Iku ngisolasi emitter saka listener-listenere — `OrderService` ora ngerti utawa ora mirsani sapa sing ngrungokake, dadi sampeyan bisa nambah reaksi (email, analytics, logging) tanpa ngowahi iku.

## Method-method sing bisa diduweni

```js
emitter.once("ready", fn);          // listener runs only ONCE, then auto-removes
emitter.off("order", fn);           // remove a listener (prevent leaks)
emitter.emit("error", new Error()); // "error" is special — throws if no listener!
emitter.listenerCount("order");
```

## Loro gotcha sing penting

```text
⚠️ Memory leaks: forgetting to remove listeners (use off/once). Node warns at >10
   listeners on one event ("possible EventEmitter memory leak").
⚠️ The "error" event: if emitted with no listener, Node THROWS and may crash —
   always attach an error listener to emitters that can error (streams!).
```

## Mangkene digunakake ing Node dhewe

```text
streams (data, end, error events), http.Server (request event),
process (SIGTERM, exit), sockets — all are EventEmitters.
```

## Apa kang penting

EventEmitter minangka dhasar arsitektur Node sing berbasis-event — ngerteni iku nerangake carane streams, servers, lan obyek process mlaku (kabeh iku emitter), lan iku alat standar kanggo komunikasi berbasis-event sing cuponan, nggayuh kod mumayu boten goyok sakibendinipun.

Ngerti API `on`/`emit`/`once`/`off`, risiko memory-leak saka listener sing ora dibuang, lan event `error` sing khusus bisa nyebabake krasis minangka penting kanggo nggunakake API Node kanthi bener lan nggawe sistem berbasis-event sing bisa dirawat kanthi apik.