JavaScript Date Reference
JavaScript Date objects are essential for handling dates, times, and timestamps in web development. Understanding their creation, manipulation, formatting, and reference behavior is crucial for reliable applications.
What is a Date Object?
- Represents a single point in time, stored as milliseconds since January 1, 1970, 00:00:00 UTC (Unix Epoch).
- Can be manipulated using get, set, and formatting methods.
- Can operate in local time or UTC depending on the method used.
const now = new Date();
console.log(now); // Thu Oct 09 2025 18:06:00 GMT+0530 (India Standard Time)
Creating Date Objects
No Arguments (Current Date & Time)
const now = new Date();
console.log(now);
Using a Date String
ISO 8601 format is recommended for consistency:
const date = new Date('2025-10-09'); // Local time
console.log(date); // 2025-10-09T00:00:00.000Z
Using Individual Components
const date = new Date(2025, 9, 9, 18, 6, 0); // Month is 0-based
console.log(date); // 2025-10-09T18:06:00.000Z
Using Milliseconds (Unix Timestamp)
const date = new Date(1760148960000);
console.log(date); // Wed Oct 08 2025 18:19:22
JavaScript Date Input Formats
| Format Type | Syntax / Example | Notes |
|---|---|---|
| ISO | "2025-10-08" | Standard, cross-browser reliable |
| ISO with Time | "2025-10-08T18:30:00" | Local time |
| ISO UTC | "2025-10-08T18:30:00Z" | UTC, ideal for APIs |
| Short (US) | "10/08/2025" | Browser-dependent |
| Long | "October 8, 2025" | Human-readable |
| Milliseconds | 1760148960000 | Calculations & storage |
JavaScript Date Output Formats
| Method | Example Output | Description |
|---|---|---|
toString() | Thu Oct 09 2025 18:06:00 GMT+0530 | Default local string |
toDateString() | Thu Oct 09 2025 | Human-readable date |
toTimeString() | 18:06:00 GMT+0530 | Time only |
toUTCString() | Thu, 09 Oct 2025 12:36:00 GMT | UTC time |
toISOString() | 2025-10-09T12:36:00.000Z | ISO 8601 UTC |
toLocaleString() | 10/9/2025, 6:06:00 PM | Localized date & time |
toLocaleDateString() | 10/9/2025 | Localized date |
toLocaleTimeString() | 6:06:00 PM | Localized time |
Date Get Methods
Retrieve parts of a date object. Local time vs UTC variants exist.
| Method | Returns | Example |
|---|---|---|
getFullYear() | Year (4 digits) | 2025 |
getMonth() | Month (0–11) | 9 (October) |
getDate() | Day of month (1–31) | 9 |
getDay() | Day of week (0–6) | 4 (Thursday) |
getHours() | Hours (0–23) | 18 |
getMinutes() | Minutes (0–59) | 6 |
getSeconds() | Seconds (0–59) | 0 |
getMilliseconds() | Milliseconds (0–999) | 0 |
getTime() | Milliseconds since epoch | 1760148960000 |
getTimezoneOffset() | Minutes difference from UTC | -330 |
Date Set Methods
Modify an existing Date object in place.
| Method | Parameters | Example |
|---|---|---|
setFullYear(year[, month, date]) | 2026, 0, 15 | Sets year, optional month/day |
setMonth(month[, date]) | 0–11, 1–31 | date.setMonth(0) → January |
setDate(date) | 1–31 | date.setDate(15) |
setHours(hours[, min, sec, ms]) | 0–23 | date.setHours(14,30) |
setMinutes(min[, sec, ms]) | 0–59 | date.setMinutes(45) |
setSeconds(sec[, ms]) | 0–59 | date.setSeconds(30) |
setMilliseconds(ms) | 0–999 | date.setMilliseconds(500) |
setTime(ms) | Milliseconds since epoch | date.setTime(1760148960000) |
Date Reference & Cloning
- Date objects are reference types. Assigning to another variable shares the same object.
- To avoid accidental updates, clone using
.getTime():
const date1 = new Date('2025-10-09T18:06:00+05:30');
const date2 = new Date(date1.getTime()); // Independent copy
date2.setDate(20);
console.log(date1.toLocaleString()); // 10/9/2025, 6:06 PM
console.log(date2.toLocaleString()); // 10/20/2025, 6:06 PM
Static Methods
| Method | Description | Example |
|---|---|---|
Date.now() | Current timestamp | 1760148960000 |
Date.parse(string) | Parse string to ms | Date.parse('2025-10-09') → 1760073600000 |
Date.UTC(year, month, …) | Milliseconds for UTC date | Date.UTC(2025, 9, 9) |
Practical Examples
Create, Get, Set, Format Dates
const date = new Date('2025-10-09T18:06:00+05:30');
// Get components
console.log(date.getFullYear()); // 2025
console.log(date.getMonth()); // 9
console.log(date.getDate()); // 9
// Set components
date.setFullYear(2026);
date.setMonth(0); // January
date.setDate(15);
date.setHours(14, 30);
console.log(date.toLocaleString('en-US')); // 1/15/2026, 2:30:00 PM
// UTC example
console.log(date.getUTCHours()); // 9
date.setUTCHours(12);
console.log(date.toISOString()); // 2026-01-15T12:00:00.000Z
Calculate Time Difference
const start = new Date('2025-10-09T18:06:00+05:30');
const end = new Date('2025-10-10T18:06:00+05:30');
const diffDays = (end - start) / (1000 * 60 * 60 * 24);
console.log(diffDays); // 1