Do something when slot does not have child nodes in lit-html

Question

I'd like to display a text when no content is on the slot.

class List extends LitElement {
  public render() {
    return slot.length === 0 
      ? html`No content is available`
      : html`<slot></slot>`;
  }
}

Answer 1

I think this may help :

render() {
   return html` <slot id="slot">No content is available</slot> 

`;}

firstUpdated(){
      const slot = this.shadowRoot.querySelector("#slot");
      this.slt = slot.assignedNodes();
      if (this.slt.length===0){
        console.log('No content is available')
      } else {
        console.log('Content available', this.slt)
      }
}

You can not slot's assigned nodes unless you render slot element. That's why first you need to render it. After there are a lot way to hide it. Another way is to dedect it at it's parents and pass the nr of slot element as property.

Demo