---
name: "up.Preview.prototype.layer"
area: "API"
kind: "Property"
parent: "up.Preview class"
url: "https://unpoly.com/api/up.Preview.prototype.layer"
---
<nav aria-label="Unpoly docs">[All docs](https://unpoly.com/index.md) · [up.Preview class](https://unpoly.com/api/up.Preview.md)</nav>

# up.Preview.prototype.layer

The [layer](https://unpoly.com/api/up.layer.md) that the previewed render pass is going to update.

When [opening a new overlay](https://unpoly.com/learn/opening-overlays.md), this property has the value `"new"`:

```js
up.preview('my-preview', function(preview) {
  if (preview.layer === 'new') {
    console.log("Opening a layer with mode", preview.renderOptions.mode)
  } else {
    console.log("Updating layer", preview.layer)
  }
})
```

---

## Return value {#return-value}

Type: [up.Layer](https://unpoly.com/api/up.Layer.md) | string