import { LitElement , html } from 'lit' ; import { property , customElement } from 'lit/decorators.js' ; import './my-second-element.js' ; @ customElement ( 'my-element' ) export class MyElement extends LitElement { @ property ( { type : Number } ) myNumber ? : number ; render ( ) { return html `
      <div>Here is ${ this . myNumber }</div>
      <div>And here is my second element:</div>
      <my-second-element></my-second-element>
    ` ; } }