JavaScript Tutorial · JavaScript Toolbox · Lesson 36 of 44

JavaScript Dates

Create dates, read their parts, do date maths and format them.

Creating dates

new Date() is the current moment. You can also build a date from parts or from an ISO string:

Example 1Try it yourself

const d = new Date(2026, 0, 15, 9, 30);   // 15 Jan 2026, 09:30 local time
console.log(d.getFullYear(), d.getMonth(), d.getDate());
console.log(d.getDay());                   // 0 = Sunday … 6 = Saturday
console.log(d.getHours(), d.getMinutes());
const iso = new Date("2026-03-01T12:00:00Z");
console.log(iso.toISOString());

Output

2026 0 15
4
9 30
2026-03-01T12:00:00.000Z

Watch out: months are zero-based — January is 0, December is 11.

Date arithmetic

Dates are stored as milliseconds since 1 January 1970 (UTC). Subtract dates to get a difference in milliseconds:

Example 2Try it yourself

const start = new Date("2026-01-01T00:00:00Z");
const end = new Date("2026-03-01T00:00:00Z");
const days = (end - start) / (1000 * 60 * 60 * 24);
console.log(days);
const due = new Date(start);
due.setUTCDate(due.getUTCDate() + 45);
console.log(due.toISOString().slice(0, 10));

Output

59
2026-02-15

Formatting

toISOString() gives a machine-friendly UTC string. For people, use Intl.DateTimeFormat or toLocaleDateString() with a locale and options:

Example 3Try it yourself

const launch = new Date(Date.UTC(2026, 6, 4, 18, 0));
const opts = { dateStyle: "full", timeStyle: "short", timeZone: "UTC" };
console.log(new Intl.DateTimeFormat("en-US", opts).format(launch));
console.log(launch.toLocaleDateString("en-GB", { timeZone: "UTC" }));
console.log(launch.toISOString());

Output

Saturday, July 4, 2026 at 6:00 PM
04/07/2026
2026-07-04T18:00:00.000Z

The built-in Date is famously awkward. The new Temporal API fixes it; until it's everywhere, libraries like date-fns and dayjs are popular.

Test yourself

What does new Date(2026, 1, 1).getMonth() return?

0
1
2
12

Show answer

Answer: 1

Months are zero-based, so month 1 is February and getMonth() returns 1.