app.js with deleteItem method added

app.js

import { htmlToElement } from './utils';

export default class App {
  //...

  addNewItem(itemName) {
    //...

    const item = htmlToElement(`
      //...
    `);

    item.getElementsByClassName('delete-button')[0].addEventListener('click', () => this.deleteItem(item));

    this.listRoot.appendChild(item);
    this.input.value = '';
  }

  deleteItem(item) {
    item.remove();
  }
}