Create a unique number with javascript time

Question

I need to generate unique id numbers on the fly using javascript. In the past, I\'ve done this by creating a number using time. The number would be made up of the four digi

Answer 1

The shortest way to create a number that you can be pretty sure will be unique among as many separate instances as you can think of is

Date.now() + Math.random()

If there is a 1 millisecond difference in function call, it is 100% guaranteed to generate a different number. For function calls within the same millisecond you should only start to be worried if you are creating more than a few million numbers within this same millisecond, which is not very probable.

For more on the probability of getting a repeated number within the same millisecond see https://stackoverflow.com/a/28220928/4617597

Answer 2

In 2020, you can use the in-browser Crypto API to generate cryptographically strong random values.

function getRandomNumbers() {
  const typedArray = new Uint8Array(10);
  const randomValues = window.crypto.getRandomValues(typedArray);
  return randomValues.join('');
}

console.log(getRandomNumbers());
// 1857488137147725264738

both Uint8Array and Crypto.getRandomValues are supported on all major browsers, including IE11

Answer 3

let now = new Date();
let timestamp = now.getFullYear().toString();
let month = now.getMonth() + 1;
timestamp += (month < 10 ? '0' : '') + month.toString();
timestamp += (now.getDate() < 10 ? '0' : '') + now.getDate().toString();
timestamp += (now.getHours() < 10 ? '0' : '') + now.getHours().toString();
timestamp += (now.getMinutes() < 10 ? '0' : '') + now.getMinutes().toString();
timestamp += (now.getSeconds() < 10 ? '0' : '') + now.getSeconds().toString();
timestamp += (now.getMilliseconds() < 100 ? '0' : '') + now.getMilliseconds().toString();

Answer 4

Easy and always get unique value :

const uniqueValue = (new Date()).getTime() + Math.trunc(365 * Math.random());
**OUTPUT LIKE THIS** : 1556782842762

Answer 5

To get a unique number:

function getUnique(){
    return new Date().getTime().toString() + window.crypto.getRandomValues(new Uint32Array(1))[0];
}
// or 
function getUniqueNumber(){
    const now = new Date();
    return Number([
        now.getFullYear(),
        now.getMonth(),
        now.getDate(),
        now.getHours(),
        now.getMinutes(),
        now.getUTCMilliseconds(),
        window.crypto.getRandomValues(new Uint8Array(1))[0]
    ].join(""));
}

Example:

getUnique()
"15951973277543340653840"

for (let i=0; i<5; i++){
    console.log( getUnique() );
}
15951974746301197061197
15951974746301600673248
15951974746302690320798
15951974746313778184640
1595197474631922766030

getUniqueNumber()
20206201121832230

for (let i=0; i<5; i++){
    console.log( getUniqueNumber() );
}
2020620112149367
2020620112149336
20206201121493240
20206201121493150
20206201121494200

you can change the length using:

new Uint8Array(1)[0]
// or
new Uint16Array(1)[0]
// or
new Uint32Array(1)[0]

Answer 6

Here's what I do when I want something smaller than a bunch of numbers - change base.

var uid = (new Date().getTime()).toString(36)