JavaScript Dates — Interview Questions & Answers

Ques: What is the Date object in JavaScript?

Ans: The Date object in JavaScript is used to work with dates and times — including years, months, days, hours, minutes, seconds, and milliseconds.

Example:

let currentDate = new Date();
console.log(currentDate);

Ques: How do you create a Date object in JavaScript?

Ans: There are 4 main ways to create a Date:

Syntax	Example	Description
new Date()	new Date()	Current date & time
new Date(milliseconds)	new Date(0)	Since Jan 1, 1970
new Date(dateString)	new Date("2025-10-27")	From string
new Date(year, month, day, hours, minutes, seconds, ms)	new Date(2025, 9, 27, 14, 0, 0)	Specific date

Ques: What are different date formats in JavaScript?

Ans: JavaScript automatically converts dates to readable formats:

let d = new Date("2025-10-27");
console.log(d.toString());     // Full string format
console.log(d.toDateString()); // Date only
console.log(d.toISOString());  // ISO standard (used in APIs)
console.log(d.toUTCString());  // UTC format

Ques: How can you get parts of a date in JavaScript?

Ans: Use Get Methods to extract specific date/time components:

Method	Description	Example
getFullYear()	Year	2025
getMonth()	Month (0–11)	9 (October)
getDate()	Day of month (1–31)	27
getDay()	Day of week (0–6)	1 (Monday)
getHours()	Hour (0–23)	14
getMinutes()	Minutes	45
getSeconds()	Seconds	30
getMilliseconds()	Milliseconds	500
getTime()	Milliseconds since Jan 1, 1970	1730018400000

Ques: How can you set parts of a date?

Ans: Use Set Methods to modify date/time values.

setFullYear(year), setMonth(month), setDate(day), setHours(hour), setMinutes(minute), setMilliseconds(ms), setSeconds(second)

Example:

let date = new Date();
date.setFullYear(2030);
date.setMonth(0); // January
console.log(date);

Ques: How do you compare two dates in JavaScript?

Ans: Convert both dates into timestamps using getTime() or direct comparison.

let d1 = new Date("2025-10-27");
let d2 = new Date("2025-12-01");

if (d1 < d2) console.log("d1 is earlier");

Ques: How do you format dates in JavaScript?

Ans: You can use:

• toLocaleDateString() → Localized date
• toLocaleTimeString() → Localized time
• Intl.DateTimeFormat → Custom formatting

Example:

let date = new Date();
console.log(date.toLocaleString("en-IN", { weekday: "long", month: "long", day: "numeric" }));

Ques: How do you get the current timestamp?

Ans: Use any of the following:

Date.now();           // milliseconds since 1970
new Date().getTime(); // same as above

Ques: What is the epoch time in JavaScript?

Ans: Epoch time is January 1, 1970, 00:00:00 UTC. All JavaScript time calculations are based on this reference point.

Ques: How do you find the difference between two dates?

Ans: Subtract one date from another — result is in milliseconds.

let start = new Date("2025-01-01");
let end = new Date("2025-12-31");

let diff = end - start;
let days = diff / (1000 * 60 * 60 * 24);
console.log(days); // 364

Ques: What is the use of Date.UTC()?

Ans: It returns a timestamp (in milliseconds) for a given UTC date and time.

let utc = Date.UTC(2025, 9, 27);
console.log(utc); // milliseconds since epoch

Ques: How do you handle time zones in JavaScript?

Ans: JavaScript dates automatically adapt to the user’s local time zone.

For global consistency, use UTC methods (getUTCDate(), setUTCHours(), etc.) or libraries like Luxon, date-fns, or Moment.js.

Ques: What are best practices when working with dates?

• Always store dates in UTC (ISO 8601) format.
• Use Date objects for time-based calculations.
• Convert to local format only when displaying.
• Avoid manual timezone calculations — use Intl or date libraries.