Добавить css link и js script динамически

const link = document.createElement('link');
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = 'https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css';
link.integrity = 'sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO'; // необязательно
link.crossOrigin = 'anonymous'; // необязательно
document.head.appendChild(link);

const script = document.createElement('script');
script.src = 'https://code.jquery.com/jquery-3.3.1.slim.min.js';
script.integrity = 'sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo'; // необязательно
script.crossOrigin = 'anonymous'; // необязательно
document.body.appendChild(script)