# Virtualization

Virtual scrolling provides an alternative to paging and is useful for displaying large sets of data.

The virtualization functionality uses a fixed amount of list items in the pop-up list of the component. While the user is scrolling the pop-up list, the ComboBox requests and displays only the visible items.

To enable virtualization, configure the [`onPageChange`](https://www.telerik.com/kendo-react-ui-develop/components/dropdowns/api/comboboxprops#onpagechange) event and the composite [`virtual`](https://www.telerik.com/kendo-react-ui-develop/components/dropdowns/api/comboboxprops#virtual) property which contains the following fields:

* `total`—Represents the number of records.
* `skip`—Represents the start of the sub-set of data which is loaded in the ComboBox.
* `pageSize`—Indicates the size of the sub-set of data.
* `onPageChange`—Provides the data for each page through the `onPageChange` event handler.

> - In order for the virtualization to work properly, the items in the popup list must have the same height. If the content of an item does not fit in a single row, the height of this item will be different from the height of the other items.
> - You also need to make sure that the `pageSize` value is equal to twice the number of visible items in the Popup.

## Basic Configuration

The following example demonstrates how to set the virtualization of the ComboBox.

[Demo Source](https://demos.telerik.com/kendo-react-ui/dropdowns/combobox/virtualization-basic/func/source.txt)

## Virtualization with Filtering

If you use virtualization in your project alongside filtering, scrolling will be reset every time the value of the filter input is changed.

[Demo Source](https://demos.telerik.com/kendo-react-ui/dropdowns/combobox/virtualization-filtering/func/source.txt)

## Virtualization with Grouping

The below example shows how we can use the ComboBox in a scenario with Grouping and Virtualization.

[Demo Source](https://demos.telerik.com/kendo-react-ui/dropdowns/combobox/virtualization-grouping/func/source.txt)

## Suggested Links

* [Virtualization with Filtering and Remote Data](https://www.telerik.com/kendo-react-ui-develop/components/dropdowns/combobox/filtering#filtering-with-remote-data-and-virtualization)
* [API Reference of the ComboBox](https://www.telerik.com/kendo-react-ui-develop/components/dropdowns/api/comboboxprops)