JavaScript Date Overview

The Date object in JavaScript is used to work with dates and times. It allows you to create dates, read components like year, month, day, hours, and perform calculations.

Date objects are static. They represent a fixed moment in time. Unlike a clock, they do not automatically update as time passes

Creating Date Objects

You can create a JavaScript Date object in multiple ways.

a) Current Date and Time

Creates a Date object representing the current date and time according to your computer’s system clock.

const now = new Date();
console.log(now);
// Example: Wed Oct 08 2025 18:19:22 GMT+0530 (India Standard Time)

b) Using a Date String

• JavaScript parses the string and creates the corresponding date.
• Supported formats include YYYY-MM-DD, Month DD, YYYY, or full datetime strings.

const date1 = new Date("October 13, 2014 11:13:00");
const date2 = new Date("2022-03-25");

c) Using Individual Components

• Parameters: year, month, day, hour, minute, second, millisecond
• Months are 0-indexed: 0 = January, 11 = December
• Overflow handling: JavaScript automatically adjusts overflowed months or days:

const date = new Date(2018, 11, 24, 10, 33, 30, 0);

new Date(2018, 15, 24); // → 2019-04-24
new Date(2018, 5, 35);  // → 2018-07-05

Number of Parameters	Meaning
2	year, month
3	year, month, day
4	year, month, day, hour
5	year, month, day, hour, minute
6	year, month, day, hour, minute, second
7	year, month, day, hour, minute, second, millisecond

One or two-digit years are treated as 19xx:

new Date(99, 11, 24); // 1999
new Date(9, 11, 24);  // 1909

d) Using Milliseconds

JavaScript internally stores dates as milliseconds since January 01, 1970 00:00:00 UTC (called Unix Epoch).

• 1 day = 86,400,000 milliseconds
• This format is useful for date calculations and comparisons.

new Date(0);                // 01 Jan 1970
new Date(86400000);         // 01 Jan 1970 + 1 day
new Date(100000000000);     // 01 Jan 1970 + 100 billion ms
new Date(-100000000000);    // 01 Jan 1970 - 100 billion ms

Displaying Dates

JavaScript provides multiple ways to display dates.

Method	Description	Example Output
toString()	Default format	Wed Oct 08 2025 18:19:22 GMT+0530
toDateString()	Human-readable date	Wed Oct 08 2025
toTimeString()	Human-readable time	18:19:22 GMT+0530
toUTCString()	UTC time	Wed, 08 Oct 2025 12:49:22 GMT
toISOString()	ISO standard	2025-10-08T12:49:22.000Z
toLocaleDateString()	Locale-specific date	10/08/2025 (US), 08/10/2025 (UK)
toLocaleTimeString()	Locale-specific time	6:19:22 PM

Example: Using Dates

// Create a specific date
const myBirthday = new Date(1995, 11, 17); // Dec 17, 1995

// Current date
const today = new Date();

// Difference in days
const diffTime = today - myBirthday; // milliseconds
const diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
console.log(`You have lived ${diffDays} days.`);