javascript - Convert current date to an Uint8 array of bytes in little endian format - Stack Overflow

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I'm trying to convert the current date to an Uint8 array of bytes in little endian format.

What I tried is this :

const epochSeconds = new Date().valueOf();

This works and returns the current date in epoch timestamp format.

I then create an array buffer of 8 bytes and a dataview and try to add the bytes to it, but it seems incorrect

const byteArray = this.longToByteArray(epochSeconds);
const buffer = new ArrayBuffer(8);
const dataView = new DataView(buffer);
for (let i = 0; i < 8; i++) {
    dataView.setUint8(i, byteArray[i]);
}

I tried to verify that value with a python program

import datetime

uint8_array = [25, 15, 142, 103, 0, 0, 0, 0]
#uint8_array = [72, 224, 87, 131, 148, 1, 0, 0]

timestamp_little_endian = int.from_bytes(uint8_array, byteorder='little')

human_readable_date_little_endian = datetime.datetime.utcfromtimestamp(timestamp_little_endian)

print(timestamp_little_endian, human_readable_date_little_endian)

With the first uint8_array i get 1737363225 2025-01-20 08:53:45 and with the second

File "a.py", line 8, in <module>
    human_readable_date_little_endian = datetime.datetime.utcfromtimestamp(timestamp_little_endian)
OSError: [Errno 22] Invalid argument

What am I doing wrong ?

I'm trying to convert the current date to an Uint8 array of bytes in little endian format.

What I tried is this :

const epochSeconds = new Date().valueOf();

This works and returns the current date in epoch timestamp format.

I then create an array buffer of 8 bytes and a dataview and try to add the bytes to it, but it seems incorrect

const byteArray = this.longToByteArray(epochSeconds);
const buffer = new ArrayBuffer(8);
const dataView = new DataView(buffer);
for (let i = 0; i < 8; i++) {
    dataView.setUint8(i, byteArray[i]);
}

I tried to verify that value with a python program

import datetime

uint8_array = [25, 15, 142, 103, 0, 0, 0, 0]
#uint8_array = [72, 224, 87, 131, 148, 1, 0, 0]

timestamp_little_endian = int.from_bytes(uint8_array, byteorder='little')

human_readable_date_little_endian = datetime.datetime.utcfromtimestamp(timestamp_little_endian)

print(timestamp_little_endian, human_readable_date_little_endian)

With the first uint8_array i get 1737363225 2025-01-20 08:53:45 and with the second

File "a.py", line 8, in <module>
    human_readable_date_little_endian = datetime.datetime.utcfromtimestamp(timestamp_little_endian)
OSError: [Errno 22] Invalid argument

What am I doing wrong ?

• javascript
• date
• endianness
• epoch

Share Improve this question Follow asked Jan 20 at 14:11 aleksshrvaleksshrv 111 silver badge 1

• @robertklep has your answer. Just divide the ECMAScript time value by 1e3 (or just remove the last 3 digits). – RobG Commented Jan 23 at 3:41

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1 Answer 1

Sorted by: Reset to default 1

The first value is a timestamp in seconds, the second one in milliseconds, which is the resolution that Javascript uses for timestamps.

More information: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/valueOf

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