How does re-rendering work?

[ccorcos]

What does this mean?

Any component that uses an atom is automagically re-rendered when its value changes.

https://reagent-project.github.io/

How does a function know to re-render?

[zjhmale]

@ccorcos just like the example shows that

(defn counting-component []
  [:div
   "The atom " [:code "click-count"] " has value: "
   @click-count ". "
   [:input {:type "button" :value "Click me!"
            :on-click #(swap! click-count inc)}]])

the div display the internal value of the atom click-count and there is a button down below to change the value of the atom. everytime you click the button to inc the value of click-count, the counting-component component will be automagically re-rendered.

[ccorcos]

I get that it does, but my question is how? How does the function know it
needs to be re-run? This isn't something that's built into clojure is it?
On Wed, Mar 30, 2016 at 20:54 (λ . λ) notifications@github.com wrote:

@ccorcos https://github.com/ccorcos just like the example shows that

(defn counting-component []
[:div
"The atom " [:code "click-count"] " has value: "
@click-count ". "
[:input {:type "button" :value "Click me!"
:on-click #(swap! click-count inc)}]])

the div display the internal value of the atom click-count and there is a
button down below to change the value of the atom. everytime you click the
button to inc the value of click-count, the counting-component component
will be automagically re-rendered.

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#224 (comment)

[mike-thompson-day8]

Github issues for Reagent are for bug reports and feature requests. Support requests and usage questions should go to the Clojure Slack channel, the ClojureScript mailing list, or the Reagent mailing list.

Your questions above will be answered if you read these 3 pages:

1. https://github.com/Day8/re-frame/wiki/Creating%20Reagent%20Components
2. https://github.com/Day8/re-frame/wiki/Using-%5B%5D-instead-of-%28%29
3. https://github.com/Day8/re-frame/wiki/When-do-components-update%3F

[ludbek]

@ccorcos
To understand how Reagent knows which component to re render when a value changes, I think you should look at following places.

1. https://github.com/lynaghk/reflex/blob/master/src/cljs/reflex/core.cljs#L18
2. https://repl.it/@ludbek/HighFractalRefactoring#main.clj

My guess is, when Reagent renders a component it keeps track of the reagent/atoms that are being dereferenced by the component. The answer to how Reagent knows which atoms are being dereferenced, see how the code in the first link extends atom to notify when it is dereferenced.

The code in the 2nd link is trying to mimic how https://github.com/mobxjs/mobx works.