Finding out the number of days until a specific date sounds tricky, but using Javascript's built-in date object we can do it easily.

First, we need to understand what the Date object is, and how it works. At it's core, the date object contains a number which represents a specific instant in time, specifically, the number of seconds since January 1, 1970. By using a number of seconds to store the time, we can easily avoid problems related to day shifts caused by leap years and daylight savings time.

Making a new Date object

Getting today's date is easy. Simply use the Date object's constructor:

 // Get today's date
const now = new Date();
// Sun Nov 13 2022 18:28:22 GMT-0500 (Eastern Standard Time)

To make a different date, for example, Christmas, you would use a different constructor, where the date is specified by a string:

// Make a date object for christmas
const christmas = new Date("Dec 25, 2022 00:00:00")

How to get the year, month, or day from the Date

Now that we have our time in a Date object, finding the Year, Month, or Day is as simple using Date's methods:

const year = christmas.getFullYear() \\ 2022
const month = christmas.getMonth()\\ 11 - Get month as a number (0-11)

Other Methods

• getFullYear() Get year as a four digit number (yyyy)
• getMonth() Get month as a number (0-11)
• getDate() Get day as a number (1-31)
• getDay() Get weekday as a number (0-6)
• getHours() Get hour (0-23)
• getMinutes() Get minute (0-59)
• getSeconds() Get second (0-59)
• getMilliseconds() Get millisecond (0-999)
• getTime() Get time (milliseconds since January 1, 1970)

Now that we know about Date's methods, getting the difference in milliseconds between two dates is as easy as:

const msUntilChristmas = christmas.getTime() - now.getTime();

Which can easily be converted to days until christmas by dividing by the number of ms per day:

const daysUntilChristmas = Math.floor(msUntilChristmas / (1000 * 60 * 60 * 24));
\\ use Math.floor() to round down
\\ 1000 ms per second
\\ 60 seconds per minute
\\ 60 minutes per hour
\\ 24 hours per day
console.log(`${daysUntilChristmas} days!`) /// 41 days!

Now you can calculate the exact number of days until Christmas, even if there is a leap year! Using the same concepts explained above, you can calculate the number of days, hours, or even minutes until, or since any day or time of your choosing!