4 ms·

apparently codepen runs the code through a parser and inserts exit checks in all detectsble loops. https://blog.codepen.io/2016/06/08/can-adjust-infinite-loop-

• greggman 9y ago
  as for why no races I think because it's basically impossible (or way too non performant) to write a JavaScript engine that can handle multiple threads deleting properties on objects. You'd have to lock on every delete.
  • Lerc 9y ago
    That's the nature of JIT though, non-performant but working is ok for the bits that might cause trouble. JavaScript should just make fast the things it can. I'd be ok for a light pre-emtion that would happen between javascript statements. Instead of genuain preemtion have the Javascript engine include break checks. A check of a flag and conditional branch (usually not taken) is not a huge expence. The cost can be especially ameliorated if you do the check only on statements that jump to earlier statements. That fixes the problem of long running code stopping other things. It doen't need system level threads or parallelism, just a js engine doing spot checks.