JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/dayjs/1.8.16/dayjs.min.js"></script>

JavaScript

date = "2020-11-30"

plus_week = dayjs(date).add(1, 'week').format("YYYY-MM-DD")

document.body.textContent = plus_week