What exactly is elegant and simple about that? I feel like this kind of syntax would break down on more complex examples, is that not the case? What would it look like with multiple conditions (say something like A && B || C)?
After all, we're not just displaying "Hello" or "Please log in" all day.
To answer you question, you use JS! Or PHP! Or any of the other 2 dozen languages Mustache supports. Mustache is all about logic-less templates, which by definition assumes the logic is being written elsewhere. Edited my example to make that clearer.
EDIT:
const tpl = "{{#loggedIn}}Hello{{userName}}{/loggedIn}}{{^loggedIn}}Please log in{{/loggedIn}}";
Mustache.render( tpl, state );There is even a ClojureScript implementation: https://github.com/fotoetienne/cljstache
Yes mustache, JSX and all the other templating syntax aren't pretty, but my point was that Mustache is the best I've come across so far. elegance and simplicity are in the eyes of the beholder though, so to each their own.