RunKit + npm: dayjs

var dayjs = require("dayjs@1.8.13") var utc = require('dayjs/plugin/utc'); dayjs.extend(utc); let x = dayjs('2019-03-09').utc().startOf('day') console.log('x:', x.format()) let y = x.add(1, 'day'); console.log('y:', y.format()) let z = y.add(1, 'day'); console.log('z:', z.format())