Minimal clojurescript reagent example

Components
Fetching a html element reference
Further reading

Components

Reagent allow multiple ways to create components with increasing complexity. There is some good info in this article. https://purelyfunctional.tv/guide/reagent/

Form 1 components

Form one components are for simply rendering some html with values that are not going to change.

In the example below the function just returns some hiccup with the parameters inserted, you need to specify :key when dynamically repeating the elements and these should be reproducible unique id's where possible not randomly generated or indexed numbers if the data is unordered.

(defn navbar-link [{:keys [href title text] :or {text nil title nil}}]
  [:a.link.dim.dib.mr3 {:key href :href href :title title} text])

[navbar-link {:href "https://clojure.org" :title "linke title" :text "link here"}]

(defn product-card
  [{:keys [title amount description link]}]
  [:article.br2.ba.dark-gray.b--black-10.ma2.w-100.w-50-m.w-25-l.mw5
   [:img.db.w-100.br2.br--top {:src link}]
   [:div.pa2.ph3-ns.pb3-ns
    [:div.dt.w-100.mt1
     [:div.dtc [:h1.f5.f4-ns.mv0 title]]
     [:div.dtc.tr [:h2.f5.mv0 amount]]]
    [:p.f6.lh-copy.measure.mt2.mid-gray description]]])

[:div.flex 
 [product-card
      {:title "Cat 01"
       :amount "£54.59"
       :description "Cat 1 description here"
       :link "http://placekitten.com/g/600/300"}]
 [product-card
      {:title "Cat 02"
       :amount "£34.59"
       :description "Cat 2 description here"
       :link "http://placekitten.com/g/600/300"}]]

Form 2 components

In form two we can track local state inside a component a click counter being a basic example.

(defn my-component [title starting-value]
  (let [local-state (reagent/atom starting-value)]
    (fn [title]
      [:h1 {:class (when @local-state "hide")
            :on-click (fn [] (swap! local-state inc))}
       (str title " " @local-state)])))

[my-component "Clickable component" 1]

Form 3 components

This form of component give's you full access to the react life cycle methods, so render did-mount did-unmount etc usually this form of component is only needed when rendering graphics or things like graphs, it's also useful for capturing errors and handling them as in the example below, which renders your components but if component-did-catch is trigger the error is caught and displayed instead.

(defn err-boundary
  [& children]
  (let [err-state (reagent/atom nil)]
    (reagent/create-class
      {:display-name "ErrBoundary"
       :component-did-catch (fn [err info]
                              (reset! err-state [err info]))
       :reagent-render (fn [& children]
                         (if (nil? @err-state)
                           (into [:<>] children)
                           (let [[_ info] @err-state]
                             [:pre [:code (pr-str info)]])))})))

Fetching a html element reference

If we wish to capture a node we can use :ref and store the result in an atom, we can then de reference the atom and call a method on the node using aget.

(defn example-ref-component [title]
  (let [local-ref (reagent/atom nil)]
    (fn [title]
      [:div#example-ref-id.flex.items-center.justify-center.pa4.bg-lightest-blue.navy
       {:ref #(reset! local-ref %)}
       (str title (when @local-ref (aget @local-ref "id")))])))

[example-ref-component "Grabbing the element id using ref "]

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