increment a date in javascript

Apr 4, 2020
2 minutes to read

Another quickie. Sometimes you want to increment a date without having to pull in the monster that is moment.js, date-fns or even the tiny day.js. Maybe you’re restricted by your environment. Whatever the reason, it never hurts to know your way around some native APIs.

Let’s say we need to display the current date and a day a fortnight from now.

If you google for this, you’ll find a StackOverflow answer

const fortnightAway = new Date( + 12096e5)

Where 12096e5 is a representation of 1000 * 60 * 60 * 24 * 14, which is 14 days in milliseconds. But we can do better.

const date = new Date()
date.setDate(date.getDate() + 14)

The important thing to note is that modifier methods on our original date property (like setDate()) modify the original date object in-place and return the new date’s value in a smilar manner as Date.getNow() would return. So whilst we could get the date again from the return value, it’s simpler to use the original date instance again.

So with this, we could implement something like

const date = new Date()
const currentDate = date.toLocaleDateString('en-GB')
date.setDate(date.getDate() + 14)
const assignmentIsDue = date.toLocaleDateString('en-GB')

Which results in these dynamic dates 👇