Try checking for existing elements in connectedCalback or by listening for slotchange events dispatched by your slot element ([HOST]Root. 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). 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. The slotted element appears, but then doesn't disappear when the dom-if becomes false. Slots allow to show elements from light DOM in specified places of shadow DOM. When working with Shadow DOM-enabled components, the element is a web platform native way to allow content projection into components. Note that when applying the restamp attribute to dom-if. There are two kinds of slots: Named slots: