The Date object in JavaScript is a powerful tool for working with dates and times. It stores the number of milliseconds that have passed since January 1, 1970, 00:00:00 UTC (the Unix Epoch). This representation allows you to perform a wide range of operations, from obtaining the current date and time to manipulating and comparing dates.

let currentDate = new Date();
    console.log(currentDate); // Displays the current date and time

Creating Date Objects

You can create Date objects using various constructors, depending on the specific date and time you want to represent.

Create a Date Object for the Current Date and Time

let now = new Date();
    console.log(now); // Current date and time

Create a Date Object with a Specific Date

let specificDate = new Date('December 25, 2024 12:00:00');
    console.log(specificDate); // Wed Dec 25 2024 12:00:00

Create a Date Object with Year, Month, Day, etc.

let newDate = new Date(2024, 11, 25, 12, 0, 0); // Month is 0-indexed (11 = December)
    console.log(newDate); // Wed Dec 25 2024 12:00:00

Create a Date Object from Milliseconds

let dateFromMillis = new Date(0); // 0 milliseconds = Jan 1, 1970
    console.log(dateFromMillis); // Thu Jan 01 1970 00:00:00

Date Methods

JavaScript provides a wide range of methods for working with Date objects. These methods allow you to retrieve date and time components, set new values, compare dates, format dates, and work with dates in different time zones.

Getting Date and Time Components

• getFullYear(): Returns the 4-digit year.
• getMonth(): Returns the month (0-11, where 0 is January and 11 is December).
• getDate(): Returns the day of the month (1-31).
• getHours(), getMinutes(), getSeconds(), getMilliseconds(): Return the respective time components.
• getDay(): Returns the day of the week (0-6, where 0 is Sunday and 6 is Saturday).

let year = new Date().getFullYear();
    console.log(year); // 2024
    
    let month = new Date().getMonth();
    console.log(month); // 9 (October)
    
    let day = new Date().getDate();
    console.log(day); // 11
    
    let now = new Date();
    console.log(now.getHours()); // e.g., 14 (2 PM)
    console.log(now.getMinutes()); // e.g., 30
    
    let weekday = new Date().getDay();
    console.log(weekday); // e.g., 5 (Friday)

Setting Date and Time Components

• setFullYear(year): Sets the year of the date.
• setMonth(month): Sets the month (0-11).
• setDate(day), setHours(), setMinutes(), setSeconds(), setMilliseconds(): Set the respective time components.

let d = new Date();
    d.setFullYear(2025);
    console.log(d); // Year is now 2025
    
    d = new Date();
    d.setMonth(5); // June
    console.log(d); // Month is now June
    
    d = new Date();
    d.setDate(15); // Set day to 15th
    d.setHours(10); // Set hour to 10 AM
    console.log(d); // Date with new day and time

Date Comparison Methods

• getTime(): Returns the number of milliseconds since the Unix Epoch (January 1, 1970).
• valueOf(): Same as getTime(), returns the primitive value of the Date object.

let timeMillis = new Date().getTime();
    console.log(timeMillis); // e.g., 1736340960223
    
    let timeValue = new Date().valueOf();
    console.log(timeValue); // e.g., 1736340960223

You can compare dates using standard comparison operators (<, >, <=, >=).

let date1 = new Date('2024-10-10');
    let date2 = new Date();
    console.log(date1 > date2); // true or false depending on the current date

Formatting Dates

• toDateString(): Returns the date portion as a human-readable string.
• toLocaleDateString(): Returns a locale-specific string representation of the date.
• toISOString(): Returns the date as a string in ISO 8601 format.

let date = new Date();
    console.log(date.toDateString()); // e.g., "Fri Oct 11 2024"
    
    console.log(date.toLocaleDateString('en-US')); // "10/11/2024" for US format
    
    console.log(date.toISOString()); // "2024-10-11T14:00:00.000Z"

Working with UTC Dates

JavaScript allows you to work with dates in UTC time instead of the local time zone. This is useful when dealing with dates that need to be consistent regardless of the user's location.

• getUTCFullYear(), getUTCMonth(), getUTCDate(): Get the date components in UTC time.
• setUTCFullYear(), setUTCMonth(), etc.: Set the date components in UTC time.

let now = new Date();
    console.log(now.getUTCFullYear()); // 2024
    console.log(now.getUTCMonth()); // 9 (October)
    console.log(now.getUTCDate()); // 11
    
    let d = new Date();
    d.setUTCFullYear(2025);
    console.log(d.toUTCString()); // Date with year set to 2025 in UTC

Special Cases

Invalid Date

If you create a Date object with invalid values, it will return "Invalid Date".

let invalid = new Date('invalid-date');
    console.log(invalid); // Invalid Date

NaN (Not-a-Number) in Date Operations

If a date operation results in a non-numeric value (e.g., subtracting two non-date objects), it will return NaN.

let invalidOp = new Date() - 'hello';
    console.log(invalidOp); // NaN

Date Calculations

Date objects allow for basic arithmetic operations, such as adding or subtracting days, months, or years. You can achieve this by using the methods that set specific date components.

Add Days

let date = new Date();
    date.setDate(date.getDate() + 5); // Add 5 days to the current date
    console.log(date);

Subtract Months

let date = new Date();
    date.setMonth(date.getMonth() - 2); // Subtract 2 months from the current date
    console.log(date);

Summary

The Date object in JavaScript is a versatile tool that empowers you to work with dates and times effectively. By understanding the fundamental concepts and mastering the various methods, you'll gain the ability to manipulate and format dates, handle time zones, and perform date calculations with precision.