# Using Emitter for Inter-Thread Communication

[Emitter](../reference/apis/js-apis-emitter.md) provides APIs for sending and processing events between threads, including the APIs for processing events that are subscribed to in persistent or one-shot manner, unsubscribing from events, and emitting events to the event queue.


To develop the Emitter mode, perform the following steps:


1. Subscribe to an event.

   ```ts
   import emitter from "@ohos.events.emitter";

   // Define an event with eventId 1.
   let event: emitter.InnerEvent = {
     eventId: 1
   };

   // Trigger the callback after the event with eventId 1 is received.
   let callback = (eventData: emitter.EventData) => {
     console.info('event callback');
   };

   // Subscribe to the event with eventId 1.
   emitter.on(event, callback);
   ```

2. Emit the event.

   ```ts
   import emitter from "@ohos.events.emitter";
   
   // Define an event with eventId 1 and priority Low.
   let event: emitter.InnerEvent = {
     eventId: 1,
     priority: emitter.EventPriority.LOW
   };
   
   let data = new Map<string, Object>();
   data.set("content", "c");
   data.set("id", 1);
   data.set("isEmpty", false);
   let eventData: emitter.EventData = {data};
   
   // Emit the event with eventId 1 and event content eventData.
   emitter.emit(event, eventData);
   ```