The Web Component Slot element - HTML - MDN Web Docs

tag in the currently loaded web page Listing 278 app def HTML files These both require custom slot functions

2 Answers 2 · use setTimeout inside the connectedCallback to postpone querying for your ul> tag in lightDOM · add an insertLI method on you

html slot attribute The HTML element—part of the Web Components technology suite—is a placeholder inside a web component that you can fill with your own markup,

html slot The slot> HTML element—part of the Web Components technology suite—is Tag omission, None, both the starting and ending tag are mandatory Permitted