What is the difference between Date(d.getTime()) and new Date(d.getTime()) in javascript?

Question

I have been working with dates and realized these 2 commands Date(d.getTime()) and new Date(d.getTime()) are different.

When I run this snippet:

        var d = new Date(2016,11,12);
        console.log(Date(d.getTime()));
        console.log(new Date(d.getTime()));

I have this result:

(index):68 Thu Dec 12 2019 18:02:41 GMT-0300 (Horário Padrão de Brasília)
(index):69 Mon Dec 12 2016 00:00:00 GMT-0200 (Horário de Verão de Brasília)

Why are they different?

I have tried to find some answers but I find none. These are some of references I have gone through:

Difference between Date(dateString) and new Date(dateString)

Why we can't call methods of Date() class without new operator

http://www.ecma-international.org/ecma-262/5.1/#sec-15.9.2

How does that first link in your question not directly answer your question? This looks like it should be closed as a duplicate of that question.... How is the second question not *also* a duplicate? — , Dec 12 '19 at 21:08
I understand one is a function that works different from an object method. But why weekday is different? — Diogo Bratti, Dec 12 '19 at 21:12

score 2 · Answer 1 · edited Dec 13 '19 at 01:42

Date gets the window/global Date object, new Date() creates a new static Date object. When you create a new Date() you are freezing its value in time.

When you use Date(), it returns a string representation of the current date as if calling new Date().toString().

Based on your code:

// this is a new date, Dec. 12, 2016
var d = new Date(2016,11,12);  

// this returns the time value of Date d
d.getTime()

// Calling Date as a function just returns a string for
// the current date, arguments are ignored
console.log(Date(d.getTime())); 

// this creates a new date based on d's time value
console.log(new Date(d.getTime()));

Salman A · Accepted Answer · 2019-12-13T07:16:05.540

0

Date(x) returns a string representing the current time, the arguments are ignored.
See date constructor called as a function in the specs. This is the expected behavior.
new Date(x) returns a Date object initialized with x.
See one-argument variant of the date constructor.

edited Dec 13 '19 at 07:16

answered Dec 12 '19 at 21:13

Salman A

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Ok, but why are they different weekdays? – Diogo Bratti Dec 12 '19 at 21:13
@DiogoBratti read the part that says "representing the current date irrespective of the argument passed to it". – Salman A Dec 12 '19 at 21:15
Ok, but why Dec 12 is Mon and Thu at same time? – Diogo Bratti Dec 12 '19 at 21:16
1

@DiogoBratti do you think Dec 12 is the same day every year? – jonrsharpe Dec 12 '19 at 21:17
@DiogoBratti It's not? 2016 is not 2019. – Dec 12 '19 at 21:19

What is the difference between Date(d.getTime()) and new Date(d.getTime()) in javascript?

2 Answers2