app.element.html

<h1>Welcome to ${title}</h1>

app.element.ts

import './app.element.scss';
import template from '!!raw-loader!./app.element.html';

export class AppElement extends HTMLElement {
  public static observedAttributes = [];

  connectedCallback() {
    const title = 'My Component';
    this.innerHTML = template.replace('${title}', title);
  }
}

customElements.define('yonatan-root', AppElement);

raw-loader.d.ts

declare module '!!raw-loader!*' {
  const contents: string
  export = contents
}

tsconfig.json

{
  "compilerOptions": {
  "types": ["raw-loader.d.ts", "node"],
  "allowSyntheticDefaultImports": true
}