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). Try checking for existing elements in connectedCalback or by listening for slotchange events dispatched by your slot element ([HOST]Root. As you can see, slot-based composition is a powerful tool that allows widgets to pull in the page content without cloning or modifying the DOM. The slotted element appears, but then doesn't disappear when the dom-if becomes false. The slot is rendered correctly and everything appears to behave, except when flicking back and forth, once the earlier slot has been rendered. Slots allow to show elements from light DOM in specified places of shadow DOM. . [HOST] › blog › introducing-shadow-dom-api. This article explains how you can use the and elements to create a flexible template that can then be used to populate the shadow DOM of a. 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. Note that when applying the restamp attribute to dom-if. There are two kinds of slots: Named slots: