JavaScript Date & Time

Date Object

Work with dates and times in JavaScript

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Working with Dates

The Date object represents a single moment in time. Create dates, get/set components, calculate differences, and format for display.

Important

JavaScript Date uses milliseconds since January 1, 1970 UTC (Unix epoch). Months are 0-indexed (0=January, 11=December).

🎓Understanding Dates

📅

What is a Date?

A specific point in time - like "December 14, 2024 at 3:30 PM"

⏱️

How JS Stores It

As milliseconds since January 1, 1970 (Unix epoch)

🔧

What You Can Do

Create, read, modify, compare, and calculate with dates

Creating a Date

new Date()

Creates date with current time

new Date('2024-12-14')

Creates date from string

new Date(2024, 11, 14)

Creates date from year, month, day (month is 0-indexed!)

Beginner Tip: Month Numbers

JavaScript counts months starting from 0:

0= January

11= December

So December 14 is written as new Date(2024, 11, 14) not new Date(2024, 12, 14)

Date Components

Date Parts:

• Year - 2024

• Month - 0-11 (January-December)

• Day - 1-31

• Day of Week - 0-6 (Sun-Sat)

Time Parts:

• Hours - 0-23

• Minutes - 0-59

• Seconds - 0-59

• Milliseconds - 0-999

Creating Dates

Different ways to create Date objects

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Get Date Components

Extract parts of a date

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Set Date Components

Modify parts of a date

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Date Arithmetic

Add/subtract days, compare dates

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Timestamps

Work with Unix timestamps

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Common Use Cases

Practical date operations

javascript

code

DarkEditable

// Check if date is today
function isToday(date) {
  const today = new Date();
  return date.getDate() === today.getDate() &&
         date.getMonth() === today.getMonth() &&
         date.getFullYear() === today.getFullYear();
}

// Check if date is in the past
function isPast(date) {
  return date < new Date();
}

// Get age from birthdate
function getAge(birthDate) {
  const today = new Date();
  let age = today.getFullYear() - birthDate.getFullYear();
  const monthDiff = today.getMonth() - birthDate.getMonth();
  
  if (monthDiff < 0 || (monthDiff === 0 && today.getDate() < birthDate.getDate())) {
    age--;
  }
  
  return age;
}

const birthDate = new Date('1990-05-15');
console.log(getAge(birthDate));  // 34

// Days until date
function daysUntil(targetDate) {
  const today = new Date();
  const diffMs = targetDate - today;
  return Math.ceil(diffMs / (1000 * 60 * 60 * 24));
}

const christmas = new Date('2024-12-25');
console.log(`Days until Christmas: ${daysUntil(christmas)}`);

// Get start/end of day
function getStartOfDay(date) {
  const newDate = new Date(date);
  newDate.setHours(0, 0, 0, 0);
  return newDate;
}

function getEndOfDay(date) {
  const newDate = new Date(date);
  newDate.setHours(23, 59, 59, 999);
  return newDate;
}

Console Output

Click "Run Code" to see output here...

Important Notes

⚠️ Months are 0-indexed

January = 0, February = 1, ..., December = 11. Always add 1 when displaying month numbers.

🌍 Time Zones

Date object uses local time zone. Use UTC methods (getUTCHours()) for consistent results.

📅 Date Parsing

Use ISO 8601 format (YYYY-MM-DD) for reliable cross-browser parsing.

Key Takeaways

Create

new Date() for current, pass string/timestamp

🔢

Months

0-indexed! January=0, December=11

⏱️

Timestamp

Date.now() or .getTime() for milliseconds

➕

Arithmetic

Subtract dates for difference, use setters to add/subtract

Previous Topic

WeakSet

Weak-reference sets for tracking objects.

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Date Methods

Getting and setting date components.

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Output

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JavaScript Date & Time

Date Object

Work with dates and times in JavaScript

Find videos you like?

Save to resource drawer for future reference!

Working with Dates

The Date object represents a single moment in time. Create dates, get/set components, calculate differences, and format for display.

Important

JavaScript Date uses milliseconds since January 1, 1970 UTC (Unix epoch). Months are 0-indexed (0=January, 11=December).

🎓Understanding Dates

📅

What is a Date?

A specific point in time - like "December 14, 2024 at 3:30 PM"

⏱️

How JS Stores It

As milliseconds since January 1, 1970 (Unix epoch)

🔧

What You Can Do

Create, read, modify, compare, and calculate with dates

Creating a Date

new Date()

Creates date with current time

new Date('2024-12-14')

Creates date from string

new Date(2024, 11, 14)

Creates date from year, month, day (month is 0-indexed!)

Beginner Tip: Month Numbers

JavaScript counts months starting from 0:

0= January

11= December

So December 14 is written as new Date(2024, 11, 14) not new Date(2024, 12, 14)

Date Components

Date Parts:

• Year - 2024

• Month - 0-11 (January-December)

• Day - 1-31

• Day of Week - 0-6 (Sun-Sat)

Time Parts:

• Hours - 0-23

• Minutes - 0-59

• Seconds - 0-59

• Milliseconds - 0-999

Creating Dates

Different ways to create Date objects

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Get Date Components

Extract parts of a date

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Set Date Components

Modify parts of a date

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Date Arithmetic

Add/subtract days, compare dates

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Timestamps

Work with Unix timestamps

javascript

code

DarkEditable

Console Output

Click "Run Code" to see output here...

Common Use Cases

Practical date operations

javascript

code

DarkEditable

// Check if date is in the past
function isPast(date) {
  return date < new Date();
}

const birthDate = new Date('1990-05-15');
console.log(getAge(birthDate));  // 34

// Days until date
function daysUntil(targetDate) {
  const today = new Date();
  const diffMs = targetDate - today;
  return Math.ceil(diffMs / (1000 * 60 * 60 * 24));
}

const christmas = new Date('2024-12-25');
console.log(`Days until Christmas: ${daysUntil(christmas)}`);

// Get start/end of day
function getStartOfDay(date) {
  const newDate = new Date(date);
  newDate.setHours(0, 0, 0, 0);
  return newDate;
}

function getEndOfDay(date) {
  const newDate = new Date(date);
  newDate.setHours(23, 59, 59, 999);
  return newDate;
}

Console Output

Click "Run Code" to see output here...

Important Notes

⚠️ Months are 0-indexed

January = 0, February = 1, ..., December = 11. Always add 1 when displaying month numbers.

🌍 Time Zones

Date object uses local time zone. Use UTC methods (getUTCHours()) for consistent results.

📅 Date Parsing

Use ISO 8601 format (YYYY-MM-DD) for reliable cross-browser parsing.

Key Takeaways

Create

new Date() for current, pass string/timestamp

🔢

Months

0-indexed! January=0, December=11

⏱️

Timestamp

Date.now() or .getTime() for milliseconds

➕

Arithmetic

Subtract dates for difference, use setters to add/subtract

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WeakSet

Date Methods

JavaScript Code Editor

Building Your Learning Module...

Date Object

Working with Dates

Important

What is a Date?

How JS Stores It

What You Can Do

Creating a Date

Beginner Tip: Month Numbers

Date Components

Creating Dates

Get Date Components

Set Date Components

Date Arithmetic

Timestamps

Common Use Cases

⚠️ Months are 0-indexed

🌍 Time Zones

📅 Date Parsing

Key Takeaways

Create

Months

Timestamp

Arithmetic

WeakSet

Date Methods

JavaScript Code Editor

Date Object

Working with Dates

Important

What is a Date?

How JS Stores It

What You Can Do

Creating a Date

Beginner Tip: Month Numbers

Date Components

Creating Dates

Get Date Components

Set Date Components

Date Arithmetic

Timestamps

Common Use Cases

⚠️ Months are 0-indexed

🌍 Time Zones

📅 Date Parsing

Key Takeaways

Create

Months

Timestamp

Arithmetic