JavaScript Date

The Date object stores a date and time.

const now = new Date();                  // current date and time
const d1 = new Date("2025-01-15");        // from text
const d2 = new Date(2025, 0, 15);         // year, month (0-11), day
const d3 = new Date(0);                   // milliseconds from 1 Jan 1970

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Get parts of a date

const d = new Date("2025-01-15T10:30:00Z");

console.log(d.getUTCFullYear());
console.log(d.getUTCMonth());
console.log(d.getUTCDate());
console.log(d.getUTCDay());
console.log(d.toISOString());

The getUTC... methods use UTC time. The normal ones (getFullYear(), getMonth(), getDate(), getDay(), getHours()) use the visitor’s local time zone. getDay() gives 0 for Sunday, so 3 here is Wednesday.

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Change a date

const d = new Date(2025, 0, 31);
d.setDate(d.getDate() + 1);   // add one day
console.log(d.getMonth(), d.getDate());

JavaScript fixes the date by itself: 31 January plus one day is 1 February (month 1, day 1).

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Compare dates and find the difference

const a = new Date("2025-01-01");
const b = new Date("2025-01-11");

console.log(a < b);
const days = (b - a) / (1000 * 60 * 60 * 24);
console.log(days);

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Format a date for display

const d = new Date("2025-01-15T10:30:00Z");

console.log(d.toLocaleDateString("en-IN", { timeZone: "UTC" }));
console.log(d.toLocaleDateString("en-US", { timeZone: "UTC", year: "numeric", month: "long", day: "numeric" }));

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Summary

• Create dates with new Date().
• Months start at 0.
• Subtract two dates to get milliseconds.
• Format with toLocaleDateString().
• Next: Error Handling.

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