JavaScript Date Object Cheatsheet

The Date object in JavaScript is used to work with dates and times. It provides methods to create, manipulate, and format date and time values.

---

Creating Dates

You can create a Date object in multiple ways:

1. Current Date and Time:

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

1. Specific Date:

   const specificDate = new Date(2024, 10, 21); // Year, Month (0-based), Day
   console.log(specificDate); // Thu Nov 21 2024

1. From a String:

   const fromString = new Date("2024-11-21T10:00:00");
   console.log(fromString); // Thu Nov 21 2024 10:00:00 GMT

1. From Timestamps (milliseconds since Unix epoch):

   const fromTimestamp = new Date(1732231200000);
   console.log(fromTimestamp); // Thu Nov 21 2024 10:00:00 GMT

---

Common Methods

Getting Date and Time

Method	Description	Example
getFullYear()	Returns the year	date.getFullYear() -> 2024
getMonth()	Returns the month (0-11)	date.getMonth() -> 10 (November)
getDate()	Returns the day of the month (1-31)	date.getDate() -> 21
getDay()	Returns the weekday (0-6, Sun=0)	date.getDay() -> 4 (Thursday)
getHours()	Returns the hour (0-23)	date.getHours() -> 10
getMinutes()	Returns the minutes (0-59)	date.getMinutes() -> 0
getSeconds()	Returns the seconds (0-59)	date.getSeconds() -> 0
getTime()	Returns timestamp in milliseconds	date.getTime() -> 1732231200000

---

Setting Date and Time

Method	Description	Example
setFullYear(year)	Sets the year	date.setFullYear(2025)
setMonth(month)	Sets the month (0-11)	date.setMonth(0) -> January
setDate(day)	Sets the day of the month	date.setDate(1) -> First day of the month
setHours(hour)	Sets the hour (0-23)	date.setHours(12)
setMinutes(minutes)	Sets the minutes (0-59)	date.setMinutes(30)
setSeconds(seconds)	Sets the seconds (0-59)	date.setSeconds(45)

---

Formatting Dates

Method	Description	Example
toDateString()	Returns date as a human-readable string	date.toDateString() -> "Thu Nov 21 2024"
toISOString()	Returns date in ISO format	date.toISOString() -> "2024-11-21T10:00:00.000Z"
toLocaleDateString()	Returns date in localized format	date.toLocaleDateString() -> "11/21/2024"
toLocaleTimeString()	Returns time in localized format	date.toLocaleTimeString() -> "10:00:00 AM"

---

Common Use Cases

1. Calculate Days Between Two Dates:

   const startDate = new Date("2024-11-01");
   const endDate = new Date("2024-11-21");
   const diffInTime = endDate - startDate; // Difference in milliseconds
   const diffInDays = diffInTime / (1000 * 60 * 60 * 24); // Convert to days
   console.log(diffInDays); // 20

1. Countdown Timer:

   const targetDate = new Date("2024-12-31T23:59:59");
   setInterval(() => {
       const now = new Date();
       const timeLeft = targetDate - now; // Milliseconds left
       const days = Math.floor(timeLeft / (1000 * 60 * 60 * 24));
       const hours = Math.floor((timeLeft / (1000 * 60 * 60)) % 24);
       const minutes = Math.floor((timeLeft / (1000 * 60)) % 60);
       const seconds = Math.floor((timeLeft / 1000) % 60);
       console.log(`${days}d ${hours}h ${minutes}m ${seconds}s`);
   }, 1000);

1. Format Current Date:

   const now = new Date();
   const formatted = `${now.getFullYear()}-${now.getMonth() + 1}-${now.getDate()}`;
   console.log(formatted); // "2024-11-21"

1. Find the Day of the Week:

   const date = new Date("2024-11-21");
   const days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
   console.log(days[date.getDay()]); // "Thursday"

1. Check Leap Year:

   const isLeapYear = (year) => {
       return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
   };
   console.log(isLeapYear(2024)); // true

1. Add/Subtract Days:

   const addDays = (date, days) => {
       const result = new Date(date);
       result.setDate(result.getDate() + days);
       return result;
   };
   console.log(addDays(new Date(), 10)); // Adds 10 days to the current date

---

Pro Tips

1. Use Date.now() to get the current timestamp directly without creating a Date object:

   console.log(Date.now()); // Timestamp in milliseconds

1. Be mindful of time zones when working with dates across regions. Use libraries like Moment.js or Day.js for advanced handling.

2. To avoid month off-by-one errors, remember that months are 0-indexed (0 = January, 11 = December).

---