Implements the "Elm architecture" in reagent.

Why realm? It's kind of a blend between reagent and elm. The library was also written with a re-frame project in mind, so re-alm seemed to be in spirit.

Define a model, events (named updates functions of type model -> model), and a view function, and pass them into our elm function to create a realm component. The point is that the model, events, and view are all local to the realm component.

Follow the elm architecture, and define the following 3 things:

• model: the initial model state
• events: a map from keywords k, to values v, which are functions of type : model -> model) to dispatch updates to the model
• view: function returning a Form-1 or Form-3 component. DOES NOT return a Form-2 component function!
  • if you want to do this, reference a new Form-2 component within the view fn.

Create elm component by defining a new function and returning a call to elm as a function (not as a component). Then, use the resulting component.

(defn row [label input]
  [:div.row
   [:div.col-md-2 [:label label]]
   [:div.col-md-5 input]])

(defn bmi-form []
  (elm {:view
        (fn [{:keys [model >dispatch >set]}]
          (let [bmi (let [{:keys [height weight]} @model]
                      (if (pos? (* height height))
                        (/ weight (* height height))
                        ""))]
            [:div
             [row "Height" [:input {:type "number" :id :height
                                    :value (:height @model)
                                    :on-change #(>set [:height] (-> % .-target .-value))}]]
             [row "Weight" [:input {:type "number" :id :weight
                                    :default-value (:weight @model)
                                    :on-change #(>set [:weight] (-> % .-target .-value))}]]
             [row "BMI" [:input {:type "number" :id :bmi :disabled true
                                 :value bmi}]]]))}))

As shown in the example, the view function is passed the model, and two functions >dispatch and >set. >dispatch takes the event keyword and any number of args. >set is syntax sugar, and defined as #(swap! model assoc-in %1 %2).

When you pass the :model prop into the resulting component, if the :raf key in the externally passed in model is greater than the :raf key in the local state, the local state will update.

When you pass the :watch-model prop into the resulting component, it will be called each time the model changes with the value of the model.

(defn parent-component []
  (let [model (r/atom {:weight 20
                       :height 100})
        _ (js/setTimeout #(swap! model assoc :height 30 :raf 1) 2000)]
    (fn [] [bmi-form {:model @model}])))

• enable specifying a validation fn for the model

Copyright © 2019 Allan Jiang

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.