# Once
## once
Adds a one-time listener for an initial occurrence of a specific event on a given layer.
```javascript
mapInstance.once(type, layerId, listener);
```
### Parameter
{% hint style="info" %}
Parameters for "once" is same as "on" or "off" function.
{% endhint %}
{% content-ref url="on-off" %}
[on-off](https://nostramap-doc.fatos.biz/fatos-api/map/map-control/on-off)
{% endcontent-ref %}
#### Example(Javascript + HTML)
```javascript
Map Event