At this point, we've already seen many examples of ClojureScript functions and their associated control flows, but we haven't really covered them in explicit detail. In this section, we'll look at various branching control flow special forms and macros, and we'll cover how to handle exceptions.
Like almost every programming language, ClojureScript uses if for basic conditional logic. if in ClojureScript is a special form rather than a function or a macro. Syntactically, if takes a predicate, a form that is evaluated and yielded if the predicate returns true, and an optional form that is evaluated and yielded if the predicate returns false. If the optional form for the false case is not supplied, it defaults to nil:
cljs.user=> (if (= 1 1) "One equals one!" "One does not equal one :(") ;; => "One equals one!" cljs.user=> (if (= 1 2) "One equals two!") ;; implicit nil return value when false ;; => nil
when like a combination of if and an implicit do...