Javascript Date Time Tips and Trics

In this tutorial, I will give you some tips and tricks about JavaScript Date.Before going to show you, some code let’s get familiar with some Terminology.

What is Unix Epoch


UNIX Epoch is a system for describing a point in time. It is the number of seconds that have elapsed since the Unix epoch, that is the time 00:00:00 UTC on 1 January 1970, minus leap seconds.
This is represented as Date (0) in JavaScript.

GMT and UTC


The Difference Between GMT and UTC. Greenwich Mean Time (GMT) is often interchanged or confused with Coordinated Universal Time (UTC). But GMT is a time zone, and UTC is a time standard.

ISO 8601 (Data elements and interchange formats)


The purpose of this standard is to provide an unambiguous and well-defined method of representing dates and times, to avoid misinterpretation of numeric representations of dates and times, particularly when data is transferred between countries with different conventions for writing numeric dates and times.

What is the time zone


Time zones are based on the fact that the Earth moves 15 degrees longitude each hour. Since there are 24 hours in a day, there are 24 standard time zones on the globe. (24 hours x 15º = 360º)
Let’s see some example.

  • The time is centred at Greenwich, UK (UTC +0). So, for example, if
    it is 2:30 PM in Greenwich (UTC) now, it will be 10:30 PM in Malaysia
    (UTC+8).
  • If it is 17:06 in Malaysia (UTC+8) now, it will be 2:36 PM in India (UTC+5:30), and 10:05 AM in the UK (UTC+0).
Now let’s write some code in javascript
const date=new Date()
If you run above code you will get following output
Tue Apr 07 2020 17:11:16 GMT+0800 (Singapore Standard Time)
Day/Week Month Date Year Hour Minute Second TimeZone
Tue APR 07 2020 17 11 16 GMT+8

Different Ways to create Date in javascript

Below table describe some ways to create Date in javascript
Date Description
new Date() Current Date/Time
new Date(timestamp) Milliseconds since Unix Epoch
new Date(string) Date String
new Date (year, month, day, hours, minutes, seconds, milliseconds Based on Date and time

How to get yesterday or tomorrow date from given date


  • Convert given Date to unix epoch
const date=new Date().getTime(); // Unix Epoch
  • Convert one day to milliseconds
const oneDayInMilliseconds=24*60*60*1000;
  • Pass current milliseconds + tomarrow to Date constructor as show below
const tomarow=new Date(date+oneDayInMilliseconds)
const yesterday=new Date(date-oneDayInMilliseconds)

Compare two dates in javascript

You can get milliseconds from these two dates and compare using javascript logical operator like >,<,===.
for example.
Let’s suppose you want to compare two dates in javascript.
const date1=new Date('07-03-2020');
const date1=new Date('08-03-2020');
function compare(date1,date2){
  return date1.getTime()>date2.getTime();
}
coconsole.log(compare(date1,date2)); // false


Get difference between two dates

If you want to get a difference (number of days) between you can use the same approach as we used in calculating the yesterday and tomorrow.
The formula for calculating days

diff=day1day2diff =|day1 -day2| // in milliseconfs
oneDayInMilliSeconds=86400000oneDayInMilliSeconds=86400000
days=diff÷oneDayInMillisecondsdays= | diff |\div oneDayInMilliseconds

Let’s uppose you want to calculate diffrence between following two dates
const date1=new Date('07-03-2020');
const date2=new Date('07-05-2020')
//Calculate difference in Unix Timestamp
const diff=date1.getTime()-date2.getTime()
const oneDayInMilliseconds=24*60*60*1000; // 24 hours X 60 mins X 60 secs X 1000 msec

const absDiiff=Math.abs(diff);
const numberOfDays=Math.floor(absDiiff/oneDayInMilliseconds);
console.log(numberOfDays); //
console.log(date2) // 2
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