Cookbooks
JavaScript
Chapter 7. Dates and Times
Calculating a date in the future or past

JavaScript:
Calculating a date in the future or past

How to:

JavaScript’s Date object is your go-to for date gymnastics. Let’s play with some examples:

// Today's date
let today = new Date();
console.log(today); // Outputs current date and time

// Calculate a date 7 days in the future
let nextWeek = new Date();
nextWeek.setDate(today.getDate() + 7);
console.log(nextWeek); // Outputs date for the same time, 7 days ahead

// Calculate a date 30 days in the past
let lastMonth = new Date();
lastMonth.setDate(today.getDate() - 30);
console.log(lastMonth); // Outputs date for the same time, 30 days ago

// Set a date 1 year in the future
let nextYear = new Date();
nextYear.setFullYear(today.getFullYear() + 1);
console.log(nextYear); // Outputs date for the same time next year

Outputs depend on when you run this code, as today is your current date-time.

Deep Dive

Before JavaScript had built-in date-manipulation functions, programmers had to manually calculate dates, accounting for variations in month lengths, leap years, and time zones—a real pain! With Date, much of this hassle goes away.

Alternatives to the native Date object include libraries like moment.js and date-fns, which offer richer syntax and solve quirks like daylight saving time bugs.

When calculating dates, remember: Date counts months from 0 (January) to 11 (December), not 1-12. And don’t forget leap years when working with February dates.

See Also

Comparing two dates