Didn't actually want to write a test myself.. but I miss Claudia confirmed it. Pretty concearning.

Synchronous / serial calls:

   import rng from './rng';
   
   const a = rng();
   console.log('a after first call: ', Array.from(a));
   
   const b = rng();
   console.log('a after second call:', Array.from(a));
   console.log('b after second call:', Array.from(b));
   
   console.log('a === b (same reference)?    ', a === b);
   console.log('a equals b (same contents)?  ', a.every((v, i) => v === b[i]));

output:

   a after first call:  [
     101, 193, 125,  19, 142,
     136, 181, 140, 209, 224,
     176, 153, 179, 248, 246,
     166
   ]
   a after second call: [
       4,  29, 48, 215, 162,  60,
      64,  23, 78, 137,   2, 186,
     230, 249, 70, 224
   ]
   b after second call: [
       4,  29, 48, 215, 162,  60,
      64,  23, 78, 137,   2, 186,
     230, 249, 70, 224
   ]
   a === b (same reference)?     true
   a equals b (same contents)?   true

and aynchronous calls:

   import rng from './rng';
   
   async function getId() {
      const bytes = rng();
      await new Promise(r => setTimeout(r, 0)); // yield to the event loop
      return Array.from(bytes);
   }
   
   const [id1, id2] = await Promise.all([getId(), getId()]);
   console.log('id1:', id1);
   console.log('id2:', id2);
   console.log('identical?', id1.every((v, i) => v === id2[i]));

output:

   id1 captured:  [
      61, 116, 151,  35, 153,
      75, 105,  15,  59, 235,
     162, 215, 224, 115,  31,
     122
   ]
   id2 captured:  [
      13,  3,  84,  28, 22, 176,
     160, 70,  67, 246,  1,  37,
      38, 61, 171,  23
   ]
   id1 after await: [
      13,  3,  84,  28, 22, 176,
     160, 70,  67, 246,  1,  37,
      38, 61, 171,  23
   ]
   id2 after await: [
      13,  3,  84,  28, 22, 176,
     160, 70,  67, 246,  1,  37,
      38, 61, 171,  23
   ]
   ---
   final id1: [
      13,  3,  84,  28, 22, 176,
     160, 70,  67, 246,  1,  37,
      38, 61, 171,  23
   ]
   final id2: [
      13,  3,  84,  28, 22, 176,
     160, 70,  67, 246,  1,  37,
      38, 61, 171,  23
   ]
   identical? true

Ask HN: We just had an actual UUID v4 collision...