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 digit year, two digit month, two digit day, two digit hour, two digit minute, two digit second, and three digit millisecond. So it would look something like this: 20111104103912732 ... this would give enough certainty of a unique number for my purposes.

It's been a while since I've done this and I don't have the code anymore. Anyone have the code to do this, or have a better suggestion for generating a unique ID?

Answer 1

Posting this code snippet here for my own future reference (not guaranteed but satisfactory "unique" enough):

// a valid floating number
window.generateUniqueNumber = function() {
    return new Date().valueOf() + Math.random();
};

// a valid HTML id
window.generateUniqueId = function() {
    return "_" + new Date().valueOf() + Math.random().toFixed(16).substring(2);
};

Answer 2

If you just want a unique-ish number, then

var timestamp = new Date().getUTCMilliseconds();

would get you a simple number. But if you need the readable version, you're in for a bit of processing:

var now = new Date();

timestamp = now.getFullYear().toString(); // 2011
timestamp += (now.getFullMonth < 9 ? '0' : '') + now.getFullMonth().toString(); // JS months are 0-based, so +1 and pad with 0's
timestamp += (now.getDate < 10) ? '0' : '') + now.getDate().toString(); // pad with a 0
... etc... with .getHours(), getMinutes(), getSeconds(), getMilliseconds()

Answer 3

This performs faster than creating a Date instance, uses less code and will always produce a unique number (locally):

function uniqueNumber() {
    var date = Date.now();

    // If created at same millisecond as previous
    if (date <= uniqueNumber.previous) {
        date = ++uniqueNumber.previous;
    } else {
        uniqueNumber.previous = date;
    }

    return date;
}

uniqueNumber.previous = 0;

jsfiddle: http://jsfiddle.net/j8aLocan/

I've released this on Bower and npm: https://github.com/stevenvachon/unique-number

You could also use something more elaborate such as cuid, puid or shortid to generate a non-number.

Answer 4

This also should do:

(function() {
    var uniquePrevious = 0;
    uniqueId = function() {
        return uniquePrevious++;
    };
}());

Answer 5

This creates an almost guaranteed unique 32 character key client side, if you want just numbers change the "chars" var.

var d = new Date().valueOf();
var n = d.toString();
var result = '';
var length = 32;
var p = 0;
var chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

for (var i = length; i > 0; --i){
    result += ((i & 1) && n.charAt(p) ? '<b>' + n.charAt(p) + '</b>' : chars[Math.floor(Math.random() * chars.length)]);
    if(i & 1) p++;
};

https://jsfiddle.net/j0evrdf1/1/

Answer 6

Assumed that the solution proposed by @abarber it's a good solution because uses (new Date()).getTime() so it has a windows of milliseconds and sum a tick in case of collisions in this interval, we could consider to use built-in as we can clearly see here in action:

Fist we can see here how there can be collisions in the 1/1000 window frame using (new Date()).getTime():

console.log( (new Date()).getTime() ); console.log( (new Date()).getTime() )
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console.log( (new Date()).getTime() ); console.log( (new Date()).getTime() )
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console.log( (new Date()).getTime() ); console.log( (new Date()).getTime() )
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VM1158:1 1469615403045

Second we try the proposed solution that avoid collisions in the 1/1000 window:

console.log( window.mwUnique.getUniqueID() ); console.log( window.mwUnique.getUniqueID() ); 
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VM1159:1 14696154132131

That said we could consider to use functions like the node process.nextTick that is called in the event loop as a single tick and it's well explained here. Of course in the browser there is no process.nextTick so we have to figure how how to do that. This implementation will install a nextTick function in the browser using the most closer functions to the I/O in the browser that are setTimeout(fnc,0), setImmediate(fnc), window.requestAnimationFrame. As suggested here we could add the window.postMessage, but I leave this to the reader since it needs a addEventListener as well. I have modified the original module versions to keep it simpler here:

getUniqueID = (c => {
 if(typeof(nextTick)=='undefined')
nextTick = (function(window, prefixes, i, p, fnc) {
    while (!fnc && i < prefixes.length) {
        fnc = window[prefixes[i++] + 'equestAnimationFrame'];
    }
    return (fnc && fnc.bind(window)) || window.setImmediate || function(fnc) {window.setTimeout(fnc, 0);};
})(window, 'r webkitR mozR msR oR'.split(' '), 0);
 nextTick(() => {
   return c( (new Date()).getTime() )  
 })
})

So we have in the 1/1000 window:

getUniqueID(function(c) { console.log(c); });getUniqueID(function(c) { console.log(c); });
undefined
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