> ## Documentation Index
> Fetch the complete documentation index at: https://docs.metz.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Events

> Sending data across flows

In metz, events are transmitted over a `Channel` and you use its capabilities through two key functions.

### `std.createChannelEmitter`

This function takes a `topic` as a parameter, creates a `Channel` for that topic and returns an emitter
which will let you dispatch events.

### `std.registerChannelListener`

This takes two params, a `topic` and a `listener`. The `listener` must return a `FlowExecutor`
With these params, whenever there's an event
on the channel for given topic, the `listener` is invoked.

For example:

```typescript theme={null}
@Injectable
class StockPriceEmitter {
	// We create the emitter when class gets instantiated
	private emitter = std.createChannelEmitter<number>('apple');

	emit() {
		const randomPrice = Math.random()*300;
		this.emitter.emit(randomPrice);
	}
}

@Injectable
class AppleAverageStockPrice {
	MAX_STORAGE = 10;
	private storedPrices: number[] = [];

	@Show
	averagePrice: number = 0;

	constructor() {
		// We register our listener at the time of instantiation
		std.registerChannelListener(
			'apple',
			std.flow("Calculate Average Apple Stock price", this).updateAverage,
		);
	}

	private addToStoredPrices(price: number) {
		if(this.storedPrices.length >= this.MAX_STORAGE) {
			this.storedPrices.splice(0, 1);
		}

		this.storedPrices.push(price);
	}

	updateAverage(price: number) {
		this.addToStoredPrices(price);

		const averagePrice = this.storedPrices.reduce((acc, cur) => acc+cur, 0) / this.storedPrices.length;
		this.averagePrice = Math.round(averagePrice);
	}
}
```

Here's what it looks like in action:

<Frame>
  <iframe width="900px" height="700px" src="https://app.metz.sh/play/0d0b90bfe8f0411dbde9f59071927be9?minimal=true" />
</Frame>

Play with the code [here](https://app.metz.sh/try?templateId=7).

<br />

And with that, we have covered all about asynchronous operations that metz has to offer.

<br />

Along the way we also learnt everything about designing systems in metz.
<br />But does it look pretty? How does one get those icons? Also, how are we able to show data?

Let's answer that in the next section!