Clojurians Log v2

Subs (which are just Reagent reactions) are disposed of automatically when the last watch on them is removed. Usually it happens when the last view that was using a sub is unmounted.

How does it affect you anyway?

I’m using day8.re-frame/undo, and my :undos? subscription is being disposed on the first undoable event that I dispatch

But I don’t understand why, because I have an undo and a redo button on my app and I don’t think they’re getting unmounted... they do get disabled however. Here’s the tutorial that I’m following where it describes what the buttons are like https://github.com/day8/re-frame-undo#the-result

OK, but how does it affect you? How do you even know that duspose! (IIRC the function) was called on the reaction?

Ok I figured out how to fix the behavior: could you explain what’s going on though? I had written my button like so: (defn undo-button [] (let [undos? @(subscribe [:undos?])] ;; only enable the button when there's undos (fn [] [:input {:type "button" :value "undo" :disabled (not undos?) :on-click #(dispatch [:undo])}]]))) Note that this deviates from the tutorial slightly, by moving the deref of my subscription into the let binding itself. With my button written this way, the subscription to :undos? gets disposed. When I do it the tutorial’s way instead, ie like so: (defn undo-button [] (let [undos? (subscribe [:undos?])] ;; only enable the button when there's undos (fn [] [:input {:type "button" :value "undo" :disabled (not @undos?) :on-click #(dispatch [:undo])}]]))) I get the correct behavior. Why does moving the @ result in this change of behavior?

The first example uses @ outside of the view function but, I think, within the Reagent's ratom context. It's expected. In short, don't use @ on subs/ratoms/reactions outside of view functions.

Ok I’ll remember that - thanks for your help