function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i] ? `<em>${values[i]}</em>` : '';
    return result + str + value;
  }, '');
}

const name = 'Sarah';
const score = 95;
const message = highlight`Hello ${name}, your score is ${score}!`;
console.log(message);