CODEWITHSUNDEEP
javascripttimestamp
user656925
user656925

Reputation:

Performance - Date.now() vs Date.getTime()

var timeInMs = Date.now();

per MDN

vs.

var timeInMs = new Date(optional).getTime();

per MDN.

Is there any difference between the two, besides the syntax and the ability to set the Date (to not the current) via optional in the second version?

Date.now() is faster - check out the jsperf

Upvotes: 168

Views: 128772

Answers (7)

jonvuri
jonvuri

Reputation: 5920

They are effectively equivalent, but you should use Date.now(). It's clearer and about twice as fast.

Edit: Source: https://jsperf.app/nimime/15

Upvotes: 83

Tobia Caneschi
Tobia Caneschi

Reputation: 69

Date.now() call the static method and this is enough to be preferred, perfoming a test:


# cat test.ts

const limit = 10000000 //ten milion
let startTime = Date.now()
let val = 0

for (let i=0; i<=limit; i++) {
    const val1 = Date.now()
}

let diff = Date.now() - startTime

console.log('Time Date.now(): ' + diff + ' ms')

startTime = Date.now()
val=0
for (let i=0; i<=limit; i++) {
    const val1 = new Date().getTime()
}

diff = Date.now() - startTime

console.log('Time with new Date().getTime: ' + diff + ' ms' )

Test execution:


# node test.ts
Time Date.now(): 818 ms
Time with new Date().getTime: 1625 ms

Date.now() is 50% faster

Upvotes: 1

han9912
han9912

Reputation: 1

Date.now() is calling the static method now() of the class Date. While new Date().getTime() can be divided into two steps:

  1. new Date(): Call the constructor() method of Date class to initialize an instance of Date class.
  2. Call getTime() method of the instance we just initialize.

MDN web docs classifies Date.now() into static method of Date, and Date.prototype.getTime() into instance method.

Upvotes: -2

SashaK
SashaK

Reputation: 165

Sometimes it's preferable to keep some time tracking variable in a Date object format rather than as just a number of milliseconds, to have access to Date's methods without re-instantiating. In that case, Date.now() still wins over new Date() or the like, though only by about 20% on my Chrome and by a tiny amount on IE.

See my JSPERF on

timeStamp2.setTime(Date.now()); // set to current;

vs.

timeStamp1 = new Date(); // set to current;

http://jsperf.com/new-date-vs-settime

Upvotes: 3

Pointy
Pointy

Reputation: 413720

These things are the same (edit semantically; performance is a little better with .now()):

var t1 = Date.now();
var t2 = new Date().getTime();

However, the time value from any already-created Date instance is frozen at the time of its construction (or at whatever time/date it's been set to). That is, if you do this:

var now = new Date();

and then wait a while, a subsequent call to now.getTime() will tell the time at the point the variable was set.

Upvotes: 148

Gregory Magarshak
Gregory Magarshak

Reputation: 2039

When you do (new Date()).getTime() you are creating a new Date object. If you do this repeatedly, it will be about 2x slower than Date.now()

The same principle should apply for Array.prototype.slice.call(arguments, 0) vs [].slice.call(arguments, 0)

Upvotes: 6

Brett Zamir
Brett Zamir

Reputation: 14345

Yes, that is correct; they are effectively equivalent when using the current time.

Upvotes: 2

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