[samstokes]

This is pretty cool. (tl;dr summary: creates a hidden iframe with a form pointing to the remote domain, submits the form, and uses postMessage to send the result back to the parent frame.)

We experimented with something similar a while ago, but found that creating and destroying all those iframes could slow down older browsers. (Our use case potentially required sending requests relatively frequently.) Have you observed anything like that with this technique?

[pyronicide]

I've not done much profiling/performance (especially on older browsers) yet. My use case for the whole thing was to do a fire and forget POST to a separate domain.

Honestly, flash might be the best solution for something like you're talking about. I was just going for something with almost no dependencies that was stupidly simple.