This causes the browser to freeze for at least a few seconds

Question

var s = "a";

for (var i = 0; i < 200000; ++i)
{
    s += s;
}

alert("DONE");

---

.NET Solutions Architect

Answer 1

What you are seeing is a current limitation in our QoS detection.

Originally, we had a very robust solution that focused on performing time checks.  This turned out to be very expensive greatly decreasing the overall performance.  We shipped a statement-based approach which is much more performant. However, it clearly is optimized too far in the other direction (less robust but with lower overhead) making it too easy to generate expensive code that avoids the QoS layer. 

The challenge is finding the correct compromise for the QoS checks. Our plan is to introduce heuristics that will better analyze code and depending upon execution either speed up or slow down the checks.  Look for improvements over the next few weeks.

-Scott