ClojureScript function to show a Bootstrap dropdown.

actions.cljs

(defn actions [array-of-funcs]
    (doseq [func array-of-funcs] (func)))

dropdown-impure.cljs

(defn show-dropdown [e]
    (this-as button
        (let [$button (js/$ button)]
            (.preventDefault e)
            (remove-dropdown)
            (.addClass (.parents $button ".dropdown") "open"))))

dropdown-pure.cljs

(defn show-dropdown [e]
    (this-as button
        (let [$button (js/$ button)]
            (actions
                (array (fn [] (.preventDefault e))
                       (fn [] (remove-dropdown))
                       (fn [] (.addClass (.parents $button ".dropdown") "open")))))))

Good point @mullr, I think I understood the original posters code being that he wanted to do all the mutations in a separate function keeping the other functions as pure as possible but then again this notion of pure is probably not inline with the functional notion of pure. While I like the idea, your post has given me a time to reflect and I'm not sure how best to solve this, but I do like delegating the mutation to a single function thereby keeping the other functions pretty clean. I haven't implemented this in my own app just yet, perhaps I'll wait to see if a more clean approach surfaces during my own development.

Sorry for the delayed response. Thanks for your comments @frankhale and @mullr.

@mullr the reason I feel my pure implementation is pure is because there are no side effects in the show-dropdown function. The side effects (preventing the default action, adding a class etc) are handled by the doseq expression. I thought this might be a slightly cleaner way of doing things.

Unless I've misunderstood your implementation you have side effects in your prevent-default! and add-dropdown-class! functions because you have two statements: one to change state and then another to set the return value of the function.

However, as you've suggested I'm not sure what this approach really buys you. I was interested in how you could write more functional code in CLJS than JS but I've found that you still end up having a lot of side effects in CLJS (mainly because of the DOM API). I thought you could hide this ugliness in my actions function but, to be honest, you could implement something like this in JS anyway.