When does Math.random() start repeating?

So I have this simple test in nodejs, I left it running overnight and could not get Math.random() to repeat. I realize that sooner or later the values (or even the whole sequence) will repeat, but is any reasonable expectancy as to when it is going to happen?

let v = {};
for (let i = 0; ; i++)
{
   let r = Math.random();
   if (r in v) break;
   v[r] = r;
}
console.log(i);