Date() vs Date().getTime()

Question

What is the difference between using new Date() and new Date().getTime() when subtracting two timestamps? (test script on jsFiddle)

Both of the following gives the same results:

var prev1 = new Date();
setTimeout(function() {
    var curr1 = new Date();
    var diff1 = curr1 - prev1;
}, 500);

var prev2 = new Date().getTime();
setTimeout(function() {
    var curr2 = new Date().getTime();
    var diff2 = curr2 - prev2;
}, 500);

Is there a reason I should prefer one over another?

No difference AFAIK `new Date()` will return the time in ms upon instantiation. — elclanrs, Mar 14 '13 at 04:30
duplicate: http://stackoverflow.com/questions/12517359/just-sytnax-date-now-vs-date-gettime — Moe, Mar 14 '13 at 04:33
@Moe I am asking `new Date()` vs `new Date().getTime()`, not `Date.now()`. — Antony, Mar 14 '13 at 04:34

score 63 · Accepted Answer · answered Mar 14 '13 at 04:31

I get that it wasn't in your questions, but you may want to consider Date.now() which is fastest because you don't need to instantiate a new Date object, see the following for a comparison of the different versions: http://jsperf.com/date-now-vs-new-date-gettime/8

The above link shows using new Date() is faster than (new Date()).getTime(), but that Date.now() is faster than them all.

Browser support for Date.now() isn't even that bad (IE9+):

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Date/now

For some reason jsperf shows that `(new Date()).getTime()` is faster, than `+ new Date();` any idea why? — Yaroslav Yakovlev, Feb 10 '14 at 00:54

Ben Glasser · Answer 2 · 2013-03-14T05:11:53.693

4

when you create a new Date() object it is automagically initialized to the current time.

From W3Schools:

new Date() // current date and time
new Date(milliseconds) //milliseconds since 1970/01/01
new Date(dateString)
new Date(year, month, day, hours, minutes, seconds, milliseconds)

The getTime() function simply returns that time.

From W3Schools:

Date.getTime() // method returns the number of milliseconds between midnight of January 1, 1970 and the specified date.

http://www.w3schools.com/jsref/jsref_obj_date.asp

edited Mar 14 '13 at 05:11

answered Mar 14 '13 at 04:31

Ben Glasser

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I'm not sure whether my reading comprehension is off or whether you aren't explaining `getTime()` correctly. It sounds like you are saying the value of getTime() will change between the time when the `Date` object is created when when the function is called. That's not what you meant, was it? – scott.korin Mar 14 '13 at 04:37

score 4 · Answer 3 · answered Mar 14 '13 at 04:42

4

Date arithmetic converts dates to Epoch time (milliseconds since Jan 1 1970), which is why functionally the two code snippets are the same.

As for which is faster, Jamund Ferguson's answer is correct.

answered Mar 14 '13 at 04:42

scott.korin

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Date() vs Date().getTime()

3 Answers3