Beginner Guide

Jon edited this page Apr 7, 2018 · 7 revisions

Want to explore by yourself?

What is Respo?

Respo is a virtual DOM library like React, built with ClojureScript to embrace functional programming.

Before start

Besides experiences on Web apps, you also need to know:

Component definition

Components are defined with a macro called defcomp:

(defcomp comp-space [w h]
  (div {:style {}}))

where div is a macro for creating virtual element for <div>.

The full code looks like:

  (:require [respo.macros :refer [defcomp div]]))

(def style-space
  {:width "1px", :display "inline-block", :height "1px"})

(defn compute [w h] (if (some? w) (assoc style-space :width w) (assoc style-space :height h)))

(defcomp comp-space [w h]
  (div {:style (compute w h)}))

Internally, defcomp will expand the expression to:

(def comp-space
  (create-comp :space
    (fn [w h]
      (fn [%cursor]
        (div {:style (compute w h)})))))

So comp-space is a function:

(comp-space nil 16)

DOM properties are divided into style event and attributes. Specify them in HashMaps or nothing:

  {:style {:color "grey"},
   :on-input (on-text-state %cursor), ; a function for each event, will explain later
   ; attributes
   {:placeholder "A name"})

Short hands

<> is a macro, like alias:

(<> span text style)

expands to

(span {:inner-text text, :style style})

Being a multiple arity macro, it also supports:

(<> span text)
(<> text)

=< is an alias for comp-space, just use it like that:

(=< 8 nil) ; (comp-space 8 nil)


A component can also be created with states. %cursor is inserted with macro defcomp so no worries.

(defn on-input [old-state %cursor]
  (fn [e dispatch! mutate!]
    (mutate! (:value e)))) ; will mutate component state(saved in global store)

(defcomp comp-demo [states]
  (let [state (or (:data states) "")] ; setting initial state with `(or nil "")`
    (input {:value state
            :on-input (on-input state %cursor)}))

(mutate! s) updates state of current component. To update parents' states, use (mutate! %cursor s) with a right %cursor(advanced topic).

Component states are not saved locally with components, but as a tree inside the store. Suppose store is:

{:states {}}

Use respo.macros/cursor-> to specify a new branch of the state tree:

(cursor-> :demo comp-demo states)

Then the state of comp-demo would be in global store:

{:states {:demo nil}}

Actually it's still {:states {}}, but it's like we got nil when you look into (:demo state).

You also need respo.cursor/mutate to update state tree in the store:

(defonce *store (atom {:states {}}))

(defn updater [store op op-data op-id]
  (case op
    :states (update store :states (mutate op-data))

The op-data in the example means "path" or "branch".

Render to the DOM

In order to render, you need to define store and states. Use Atoms here since they are the data sources that change over time:

(defonce *store (atom {:states {}}))

(defn id! [] (.valueOf (js/Date.))

(defn dispatch! [op op-data]
  (let [op-id (id!))
        new-store (updater @*store op op-data op-id)]
    (reset! *store new-store)))

(def mount-target (.querySelector js/document "#app"))

(defn render-app! []
  (let [app (comp-container @*store)]
    (render! mount-target app dispatch!)))

Note that you need to define dispatch! function by yourself.

Rerender on updates

Better to render on page load and changes of data sources:

(defn main! []
  (add-watch global-store :rerender render-app!))

(set! (.-onload js/window) main!)

To cooperate with hot swapping:

(defn reload! []

Notice that clear-cache! is from respo.core and it clears component caches after code updated. Caching is a mechanism to speed up virtual DOM rendering. It's invalidated after code changes.

Handling events

To make state update, you need to pass a function to :input field in :on. This function will be called with parameters of event(wrapped in :original-event of e), dispatch!(function we defined before), mutate!. mutate! changes a component state:

(defn on-text-change [old-state]
  (fn [e dispatch! mutate!]
    (mutate! (:value e))))

  {:value (:text task)
   :style style-input
   :on-input (on-text-change old-state)})

To handle a global action, call dispatch! with an action type and a parameter:

(defn handle-remove [props]
  (fn [e dispatch! mutate!]
    (dispatch! :remove (:id (:task props)))))

  {:style style-button,
   :on-click (handle-remove props)}
  (<> span "Remove" nil))

dispatch! will cause a change in *store. Also note previously :on was :event.

Composing component

Reusing components is easy. They are wrapped functions that return components:

  {:style style-task}
  (comp-debug task {:left "160px"})
  (button {:style (style-done (:done task))})
  (comp-space 8 nil)
    {:value (:text task)
     :style style-input
     :on-input (on-text-change props state)})
  (comp-space 8 nil)
    {:style style-time}
      {:inner-text (:time state)
       :style style-time})))

Compile and run

You may need a shadow-cljs.edn to configure the compiler:

{:source-paths ["src"]
 :dependencies [[mvc-works/hsl "0.1.2"]
                [respo/ui      "0.3.4"]
                [respo         "0.8.16"]]
 :builds {:app {:output-dir "target/"
                :asset-path "."
                :target :browser
                :modules {:main {:entries [app.main]}}
                :devtools {:after-load app.main/reload!
                           :http-root "target"
                           :http-port 7000}}}}

then you can compile it:

shadow-cljs watch app

Find the more in

Create an HTML with <script src="main.js"></script> in target/ to run it. shadow-cljs would start an HTTP server on http://localhost:7000 .

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