Create a unique number with javascript time

A better approach would be:

new Date().valueOf();

instead of

new Date().getUTCMilliseconds();

valueOf() is "most likely" a unique number. http://www.w3schools.com/jsref/jsref_valueof_date.asp.

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.getMonth < 9 ? '0' : '') + now.getMonth().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()

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