Collisions when generating UUIDs in JavaScript

Muxa_10793 0
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This relates to this question. I am using the code below from this answer to generate a UUID in JavaScript:

'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    var r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);
    return v.toString(16);
});

This solution appeared to be working fine, but I am getting collisions. Here's what I have:

  • A web application running in Google Chrome.
  • 16 users.
  • about 4000 UUIDs have been generated in the past two months by these users.
  • I got about 20 collisions - e.g., a new UUID generated today was the same as about two months ago (different user).

What is causing this issue and how can I avoid it?

collision uuid random javascript
6 Answers

The answers here deal with "what's causing the issue?" (Chrome Math.random seed issue) but not "how can I avoid it?".

If you are still looking for how to avoid this issue, I wrote this answer a while back as a modified take on Broofa's function to get around this exact problem. It works by offsetting the first 13 hex numbers by a hex portion of the timestamp, meaning that even if Math.random is on the same seed it will still generate a different UUID unless generated at the exact same millisecond.

user_5085370
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