Yes, I would have all frames under the same URL.
It seems to save a decent amount of typing if I just submit a form to an iframe, get the contents of the frame document, and do whatever I need with them on the parent page. (Display errors with the form after submission, for example)
So why not just submit to a frame instead of AJAX?
EDIT: https://stackoverflow.com/a/362743/870729
While iframes are meant for content embedding, one must remember that they are used quite often for other reasons. One example would be a dynamic upload form, that displays the upload progress with jQuery or something.
In my case specifically, when a user submits a form, I want to return ONE number.
For example, if the user submits the signin form, and the result is 0, the username they entered does not exist. 1 would be an incorrect password, etc.
I would do something like this in JS then:
if(response==2){ //let's just say that '2' is "no errors"
displayMessage("You have signed in successfully!");
}
EDIT:
Thank you everybody for your answers. I will just use AJAX in this case. Special thanks to @cale_b.