javascript ObjectId generator

gistfile1.js

var mongoObjectId = function () {
    var timestamp = (new Date().getTime() / 1000 | 0).toString(16);
    return timestamp + 'xxxxxxxxxxxxxxxx'.replace(/[x]/g, function() {
        return (Math.random() * 16 | 0).toString(16);
    }).toLowerCase();
};

The code has a bug, because if random resulted 1 then (Math.random() * 16 | 0).toString(16) will result "10" which is two characters, leading to invalid ObjectId that is supposed to be 24 characters long.

This random string generate function is +50% faster than the method used in the function above (measured by jsben.ch).

function getRandomString(length) {
    var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    var randS = "";

    while(length > 0) {
        randS += chars.charAt(Math.floor(Math.random() * chars.length));
        length--;
    }
    return randS;
}

Ps: generated string will contain uppercase characters, remove upper characters in var chars if you don't want them

Thanks! ;)

Cool thank you! :) 👍

Thank you so much.

👍 Good job

Thanks!

The code has a bug, because if random resulted 1 then (Math.random() * 16 | 0).toString(16) will result "10" which is two characters, leading to invalid ObjectId that is supposed to be 24 characters long.

Math.random() returns [0, 1), inclusive of 0, but not 1.

this code from bson may more useful
https://github.com/mongodb/js-bson/blob/dc9c1bb284a6c08e07f14e700bdbfb0fd57e5a13/lib/objectid.js#L154

Based on the above comments I did a sh alias
alias objectidgen='node -e "console.log((function objectidgen(length = 16) {var timestamp = (new Date().getTime() / 1000 | 0).toString(16);return timestamp + \"xxxxxxxxxxxxxxxx\".replace(/[x]/g, _ => (Math.random() * 16 | 0).toString(16)).toLowerCase();})())"'
For macOS users:
alias objectidgen='node -e "console.log((function objectidgen(length = 16) {var timestamp = (new Date().getTime() / 1000 | 0).toString(16);return timestamp + \"xxxxxxxxxxxxxxxx\".replace(/[x]/g, _ => (Math.random() * 16 | 0).toString(16)).toLowerCase();})())" | pbcopy'

Thanks! This code useful for me!

Thank you so much man!!!

Thank you so much man!!!

I appreciate that you shared this. It is a simple, logical function and integrates nicely with my Express backend.

@solenoid what about the collision of this random id generation method?

Perfect, thanks!!

simple and quick solution. thanks

here is the function in coffee script:
mongoObjectId: () ->
timestamp = ((new Date).getTime() / 1000 | 0).toString(16)
timestamp + 'xxxxxxxxxxxxxxxx'.replace(/[x]/g, ->
(Math.random() * 16 | 0).toString 16
).toLowerCase()

It saved my life. lol

Thanks dude!

Thanks!

https://observablehq.com/@hugodf/mongodb-objectid-generator

Thanks a lot, it was very useful!

I made a Golang version for a project

func mongoObjectId() string {
	ts := time.Now().UnixMilli() / 1000
	id := strconv.FormatInt(ts, 16)
	for i := 0; i < 16; i++ {
		id += fmt.Sprintf("%x", rand.Intn(16))
	}
	return id
}

Impl in rust:

use chrono::Utc;
use rand::Rng;
use std::fmt;

fn mongo_object_id() -> String {
    let ts = Utc::now().timestamp_millis() / 1000;
    let mut id = format!("{:x}", ts);
    
    for _ in 0..16 {
        let random_digit = rand::thread_rng().gen_range(0..16);
        id.push_str(&format!("{:x}", random_digit));
    }

    id
}

fn main() {
    let object_id = mongo_object_id();
    println!("{}", object_id);
}

// [dependencies]
// chrono = "0.4"
// rand = "0.8"

A simple python implementation

import time
import random

def mongo_object_id():
    timestamp = hex(int(time.time()))[2:]
    rest = ''.join([random.choice('0123456789abcdef') for _ in range(16)])
    
    return (timestamp + rest).lower()

I use console.log(new (require('bson').ObjectId)().toString()).