fromUnixTime ignored milliseconds

[dd-han]

Hi

When I using date-fns convert Unix Timestamp to JavaScript Date Object. But milliseconds seem to be ignored, code:

datefns = require('date-fns')
datefns.fromUnixTime(0.1).getMilliseconds()
// output: 0
// but expect output: 100

https://github.com/date-fns/date-fns/blob/master/src/fromUnixTime/index.js#L29

[minitesh]

@dd-han
It is because fromUnixTime() expects timestamp in seconds and converts it into milliseconds by multiplying timestamp by 1000.
So in your case 0.1 gets converted to 100 (i.e. 0.1 * 1000 => 100) so you are getting milliseconds as 0.

But even JavaScript Date will also give you the same result.

const d = new Date(0.1); // Thu Jan 01 1970 05:30:00 GMT+0530 (India Standard Time)
d.getMilliseconds(); // 0

@leshakoss @kossnocorp shouldn't the function fromUnixTime() providing support for timestamp in milliseconds along with seconds rather than expecting argument in seconds and converting it to milliseconds?

[fturmel]

shouldn't the function fromUnixTime() providing support for timestamp in milliseconds along with seconds rather than expecting argument in seconds and converting it to milliseconds

The Date constructor already supports timestamps in ms, so I think this request doesn't make much sense.

const date = new Date(100)
console.log(date.toISOString()) // '1970-01-01T00:00:00.100Z'
console.log(date.getMilliseconds()) // 100, the ms component only of the date created
console.log(date.getTime()) // 100, ms since epoch

new Date(0.1) would be a tenth of a millisecond after ECMAScript epoch, which is a lower resolution than the Date object supports. You'll just get the same result as new Date(0) which is 1970-01-01T00:00:00.000Z.

[fturmel]

Oh hold on, let me re-open this. Do you mean that the fromUnixTime function shouldn't drop the decimals, that way they could be used to represent milliseconds?

Essentially, these two lines should match instead of truncating the decimal values?

import { fromUnixTime } from "date-fns";

const ms = 1640888727872;
const sec = ms / 1000;

console.log(new Date(ms).toISOString());      // 2021-12-30T18:25:27.872Z
console.log(fromUnixTime(sec).toISOString()); // 2021-12-30T18:25:27.000Z

There is a specific unit test for this, so it seems like it was intentional and behaving this way since it was introduced by #937.

date-fns/src/fromUnixTime/test.ts

Lines 17 to 20 in 871ea7a

	it('discards decimal values', function () {
	const result = fromUnixTime(1330515499.75)
	assert(result.getTime() === 1330515499000)
	})

I assume it would be treated as a breaking change, but maybe this could be considered for v3? @tan75

[tan75]

hi all,

it is currently open for discussion.

[italosantana]

@tan75 some update?