JavaScript - difference between Date(), new Date(), and ISODate

Question

I've seen various versions of this question, but none of them answer my needs.

I want to create an ISODate for MongoDB and I'm using Node.js.

In Node, when I do:

console.log(Date());

I get:

Mon Sep 26 2016 15:17:04 GMT-0400 (EDT) <-- This is correct.

When I do:

console.log(new Date());

I get:

2016-09-26T19:17:04.731Z <- This is 4 hours ahead

My understanding of the way to do ISODATE is:

var isodate = new Date().toISOString()
console.log(isodate);

Which yields a time 4 hours ahead of "now".

My system date is correct. I run this one different machines, and I get the same results.

Can someone please explain why I'm getting a discrepancy in time?

Answer 1

The difference is that 2016-09-26T19:17:04.731Z related to GMT0 timezone and Mon Sep 26 2016 15:17:04 GMT-0400 (EDT) to your local timezone. Both are point to the same time :)

You can read more about data formats and timezones in Wiki

Answer 2

With a basic definition to the difference between Date() and new Date() is :

• Date() ignores any argument(s) passed to it and is equivalent of new Date().toISOstring()

• new Date(Optional_arguments) creates an time type object in JS on which you can perform :

• getTime() other Date.prototype functions listed on MDN Website

• Date() is just a string representation of local time.

  • new Date() gives you a manipulatable object to fiddle around.

Answer 3

Notice the Z at the end of 2016-09-26T19:17:04.731Z? It stands for Zulu, meaning UTC timezone (which is GMT+000).

As you can see in your original date string, Mon Sep 26 2016 15:17:04 GMT-0400 (EDT) has a GMT-0400 timezone, which I guess is the local time where you live. So, in fact there is no problem, just different representations of the same time:

• Date() creates a Local date
• new Date() creates a UTC date