JavaScript Dates

new Date() is now

new Date() builds a Date object for this instant on the machine that runs the script. Call it again a second later and you get a later time. There is no import.

Logging a Date prints a long string. For a clock or a filename stamp you read the pieces with getters and join them yourself.

Year, month, and day

getFullYear() is the four-digit year. getDate() is the day of the month (1 to 31).getDay() is the weekday as a number (0 is Sunday). Those two names are easy to mix up.

getMonth() is zero-based: January is 0, December is 11. Add 1 when you display a calendar month.

const now = new Date();
const year = now.getFullYear();
const month = now.getMonth() + 1;
const day = now.getDate();

console.log(now);
console.log(year);
console.log(month);
console.log(day);

document.body.textContent = year + "-" + month + "-" + day;

Hours, minutes, seconds

getHours() uses a 24-hour clock from 0 to 23. getMinutes() andgetSeconds() run from 0 to 59. A clock face usually wants two digits, so pad single digits with a leading zero.

function twoDigits(n) {
  return String(n).padStart(2, "0");
}

const now = new Date();
const clock =
  twoDigits(now.getHours()) + ":" +
  twoDigits(now.getMinutes()) + ":" +
  twoDigits(now.getSeconds());

console.log(clock);
document.body.textContent = clock;

Build a stamp

ISO-style stamps are year, month, day, then time, with hyphens and colons. You control the order. JavaScript will not invent your product’s date format for you.

function twoDigits(n) {
  return String(n).padStart(2, "0");
}

const now = new Date();
const stamp =
  now.getFullYear() + "-" +
  twoDigits(now.getMonth() + 1) + "-" +
  twoDigits(now.getDate()) + " " +
  twoDigits(now.getHours()) + ":" +
  twoDigits(now.getMinutes());

console.log(stamp);
document.body.textContent = stamp;

Specific dates and timestamps

new Date(year, monthIndex, day) builds a local date. Remember the month index is still zero-based: new Date(2026, 0, 1) is 1 January 2026.

getTime() returns milliseconds since 1 January 1970 UTC. Subtract two timestamps to get a duration in milliseconds. Divide by 1000 for seconds.

const start = new Date(2026, 0, 1);
const now = new Date();
const ms = now.getTime() - start.getTime();
const days = Math.floor(ms / 1000 / 60 / 60 / 24);

console.log(start.toString());
console.log(ms);
console.log(days);

document.body.textContent = "days since 1 Jan 2026: " + days;

Getters you will use

What to remember

• new Date() is the current instant.
• Month is 0–11. Day-of-month is getDate(), not getDay().
• Format a clock or stamp by joining padded pieces.
• getTime() is the value you subtract to measure duration.

Next: the Math object — round, floor, ceil, max, min, and abs, with nothing to import.