# 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="/pages/-MLBq0psqTwaCUghrUDG" %}
[On/Off](/fatos-api/map/map-control/on-off.md)
{% endcontent-ref %}
#### Example(Javascript + HTML)
```javascript
Map Event
```
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