I have a section on my site which i wish to be able to change and subsiquently change every page with that same content, is there a way to do this without php or an iframe?

Can i ask why do you not want to use php?

 

Alternatively you can use ajax or json to load external content (say part of a .html file, or a .txt file)

Stay away from iframes as your website won't be easily crawlable by search engines. The easiest way would probably be to use PHP includes or something along those lines.