add-days-date-fns
HTML
<script src="https://cdnjs.cloudflare.com/ajax/libs/date-fns/2.0.0-alpha0/date_fns.min.js"></script>
JavaScript
let aWeekLater = dateFns.addDays(new Date(), 7);
console.log(`Date after a week is ${aWeekLater.toDateString()}`);
const aWeekAfter1Jan2022 = dateFns.addDays(new Date('2022-01-01'), 7);
console.log(`Date after a week of 2022-01-01 is ${aWeekAfter1Jan2022.toDateString()}`);