Recently I had to learn a little bit about CORS (cross origin resource sharing). I had sites on different domains I had to get data in between. I like to try to be forward thinking, so when I learned about a better option than JSONP, I jumped all over it. Nicholas Zakas explains is very well on his article about CORS. Like all the other new, fun technologies, it's not supported by all older browsers. So I had to find a way to be forward thinking but have a fallback. What I ended up with is a CORS xhr that falls back to JSONP if CORS is not natively supported.