Working with Dates & Times

Creating Dates

const now  = new Date();           // current date/time
const d1   = new Date("2026-07-04"); // from ISO string
const d2   = new Date(2026, 6, 4);   // year, month(0-indexed), day
const ts   = Date.now();             // milliseconds since epoch

console.log(now.toISOString());      // "2026-07-04T12:00:00.000Z"

Getting Date Parts

const d = new Date("2026-07-04T15:30:00");
console.log(d.getFullYear());  // 2026
console.log(d.getMonth());     // 6 (July — 0-indexed!)
console.log(d.getDate());      // 4
console.log(d.getDay());       // 6 (Saturday — 0=Sunday)
console.log(d.getHours());     // 15
console.log(d.getMinutes());   // 30

Date Arithmetic

const start = new Date("2026-01-01");
const end   = new Date("2026-12-31");

const diffMs   = end - start; // timestamps subtract fine
const diffDays = diffMs / (1000 * 60 * 60 * 24);
console.log(diffDays); // 364

// Add 30 days
const future = new Date(start);
future.setDate(future.getDate() + 30);
console.log(future.toDateString()); // "Thu Jan 31 2026"

Formatting with Intl.DateTimeFormat

The Intl API provides locale-aware formatting:

const d = new Date("2026-07-04");

const fmt = new Intl.DateTimeFormat("en-MY", {
  dateStyle: "full",
  timeStyle: "short",
  timeZone: "Asia/Kuala_Lumpur",
});
console.log(fmt.format(d));
// "Saturday, 4 July 2026 at 08:00 am"

Relative Time with Intl.RelativeTimeFormat

const rtf = new Intl.RelativeTimeFormat("en", { numeric:"auto" });

console.log(rtf.format(-1, "day"));   // "yesterday"
console.log(rtf.format(3, "week"));   // "in 3 weeks"
console.log(rtf.format(-2, "month")); // "2 months ago"