Google Apps Script send email with html body

htmlMail.gs

function sendMail() {
  const subject = 'Subject';
  const message = 'Message';
  const templ = HtmlService.createTemplateFromFile('email'); // filename is email.html
  const htmlMessage = templ.evaluate().getContent();
  const options = { htmlBody: htmlMessage };

  GmailApp.sendEmail(respondentEmail, subject, message, options);
}