How to retrieve html elemets from another domain?

There's the situation:

My content.js runs on domain A, but need to fetch html code from another page, in another domain B.

I know that due to Same-origin policy it would be not possible, but when i read about JSONP and sending message from web page i got some doubts. I admit that these doubts are still there, because I am not quite clear about the situation.

Is there any way to do this(without using jquery)?