Creating a Javascript Templating Engine

Yea there's a lot more to it, I'm looking at this as the fundamentals. If I can't make the fundamentals enjoyable nobody will use the rest of it.

Includes are kinda rough in javascript because they require a separate http request, and would get out of hand if they're used as frequently as they are in server side templating. I need to implement some type of front-end caching, but need a way to distinguish which templates are in memory and which require a request. Thoughts are appreciated.