Atoms can't be initiated in a function or a let?

[Frozenlock]

(def at (atom "hello"))

[my-awesome-widget at]

Works as expected.
However, if I try to create the atom in a function, or in a let, it doesn't work.

[my-awesome-widget 
  (let [aa (atom "hello")]
    aa)]

In the latter case, it seems that any attempt to change the atom (from within my-awesome-widget) will fail.

[holmsand]

That's because you create a new atom every time my-awesome-widget runs in the second example, which means that it will always have the value "hello".

To make it convenient to use local atoms like that, Reagent allows you to return a new function from the component, that will be called in the future when the component has changed. Like this:

(defn timer-component []
  (let [seconds-elapsed (atom 0)]
    (fn []
      (js/setTimeout #(swap! seconds-elapsed inc) 1000)
      [:div
       "Seconds Elapsed: " @seconds-elapsed])))

The returned function will be called with exactly the same arguments as the top-level function.

You can see that in action here: http://holmsand.github.io/reagent/index.html

[Frozenlock]

Ah! Of course!
And I already read this tutorial. Shame that I forgot about this after only a few hours.

My apologies, seems like some of my Clojure reflexes are hard to shed. ;-)

Thanks for Reagent by the way, it's amazing!