bits = crypto.getRandomValues(new Uint8Array(20))

bits[5] = (bits[5] & 0x4F) | 0x40;

bits[8] = (bits[8] & 0xBF) | 0x80;

bits = [...bits].map(e => e.toString(16).padStart(2,'0') ).reduce((a,c,i)=>a+([4,7,10,13].includes(i)?'-':c));

Array(20).fill(0).map(()=>crypto.getRandomValues(new Uint8Array(1))[0].toString(16).padStart(2,'0')).reduce((a,c,i)=>a+([4,7,10,13].includes(i)?'-':c))

​

([1e3]+-10+-10+-1e5).replace(/\d/g, () => crypto.getRandomValues(new Uint8Array(1))[0].toString(16).padStart(2,'0'))

​

let s=[]; crypto.getRandomValues(new Uint8Array(20)).map( e => s.push(e.toString(16).padStart(2,'0')) ); [4,7,10,13].map( idx => s[idx]='-' ); s.join('');

​