In Magento 2 admin grid system, the one that uses ui-components, while the content of the grid is loading there is a spinner over the grid content.
.
When the grid is loaded, the spinner goes away.
What's the code js that makes it disappear when the grid contents are loaded?
magento\vendor\magento\module-ui\view\base\ui_component\templates\listing\default.xhtml
& Examplemagento\vendor\magento\module-cms\view\adminhtml\ui_component\cms_block_listing.xml
file's<item name="spinner" xsi:type="string">cms_block_columns</item>