Try checking for existing elements in connectedCalback or by listening for slotchange events dispatched by your slot element ([HOST]Root. When working with Shadow DOM-enabled components, the element is a web platform native way to allow content projection into components. To access children assigned to slots in your shadow root, you can use the standard [HOST]edNodes or [HOST]edElements methods with the slotchange event. [HOST] › blog › introducing-shadow-dom-api. A slot is a placeholder inside a web component that users can fill with their own markup (see Using templates and slots for more information). There are two kinds of slots: Named slots: