freactive

pronounced "F-reactive". This library should be considered experimental - it has not been widely tested.

freactive is a high-performance, pure Clojurescript, declarative DOM library. It uses hiccup-style syntax and Clojure's built-in deref and atom patterns. It is inspired by work done in [reagent[(https://github.com/reagent-project/reagent), om and reflex (as well as desktop GUI frameworks like QML and JavaFX). See it in action.

Goals:

Provide a dead-simple API that is intuitive and almost obvious for those familiar with Clojure (similar to Reagent)
Allow for high-performance rendering good enough for animated graphics based on a purely declarative syntax
Allow for reactive binding of any attribute, style property or child node
Provide a deeply-integrated animation framework
Allow for coordinated management of state via cursors (as in Om)
Allow for cursors based on paths as well as lenses
Provide a generic items view component for efficient viewing of large data sets
Minimize unnecessary triggering of update events
Coordinate all updates via requestAnimationFrame wherever possible
Be written in pure Clojurescript

Two-minute tutorial

lein dependency:

Hello World example:

(ns example1
  (:refer-clojure :exclude [atom])
  (:require [freactive.core :refer [atom]
            [freactive.dom :as dom)
  (:require-macros [freactive.macros :refer [rx]))
    
(defonce mouse-pos (atom nil))

(defn view []
  [:div
    {:width "100%" :height "100%"
     :on-mousemove (fn [e] (reset! mouse-pos [(.-clientX e) (.-clientY e)]))}
    [:h1 "Hello World!]
    [:p "Your mouse is at: " (rx (str @mouse-pos))]])

(defonce root (dom/append-child! (.-body js/document) [:div#root]))

(dom/mount! root (view))

If you already understand hiccup DOM syntax and Clojure's atom, you're 90% there. In freactive, make sure you use freactive's reactive atom which allows derefs to be captured by an enclosing reactive expression (this is exactly the same idea as in reagent). We just need to introduce one additional concept - the macro rx (for reactive expression).

The rx macro returns an IDeref instance (can be deref'ed with @) whose value is the body of the expression. This value gets updated when (and only when) one of the dependencies captured in its body (reactive atoms, other rx's and also things like cursors) gets "invalidated". (Pains were taken to make this invalidation process as efficient and configurable as possible.)

Passing an rx or reactive atom (or any IDeref instance) as an attribute, style property or child of a DOM element represented via a hiccup vector binds it to that attribute, style property or child node position. freactive makes sure that any updates to rx's or atom's are propogated to the DOM directly to the binding site only as often as necessary (coordinated with requestAnimationFrame).

Components are mounted by passing a target node and hiccup vector to the mount! function (this will replace the last child of the target node with the mounted node!). A few additional convenience functions are included - append-child!, remove!, and listen! - but it is encouraged to use them sparingly and prefer the declarative hiccup syntax wherever possible.

Animations

Transitions

Transition callbacks can be added to any DOM element using the with-transitions function.

(with-transitions
  [:h1 "Hello World!"]
  {:on-show (fn [node callback] (animation/animate! node 1000 my-easing-fn {:opacity "100%"} callback)})

The framework understands the :on-show and :on-hide transitions. These transitions will be applied upon changes at binding sites - i.e. at the site of an rx or an initial mount!. (A mechanism for triggering transitions based on changes to data-state is also planned.

Easers

easer's are the basis of freactive animations. An easer is a specialized type of deref value that is updated at every animation frame based on an easing function and target and duration parameters. Essentially it provides "tween" values. Easers are defined with the easer function which takes an initial value. They can be transitioned to another value using the start-easing! function which takes the following parameters: from (optional), to, duration, easing-fn and a on-complete callback.

An easer is designed to be used as a dependency in a reactive computation, like this:

(def ease-factor (easer 0.0))
(defn my-view []
  (with-transitions
    [:h1 {:opacity (rx (* 100 @ease-factor))
          :font-size (rx (* 16 @ease-fator))} "Hello World!"]
    {:on-show (fn [node callback] (start-easing! easer 0 1.0 1000 easing/quad-in on-complete)}))

Easing functions: an easing function, f, is a function that is designed to take an input t parameter that ranges from 0.0 to 1.0 that has the property (= (f 0) 0) and (= (f 1) 1). Basically the easer is supposed to smoothly transition from 0 to 1. The easer, takes care of scaling the values based on duration and from and to values. A selection of easing functions from Dan Kersten's ominate (thank you!) is currently included in this library, but this is subject to change.

Optional from parameter: the optional from parameter to start-easing! has a special behavior - if the current value of the easer is different from from, the duration of easing will be adjusted (linearly for now) based on the difference bettween from and the current value. This is to keep the speed of easing somewhat consistent. If you, don't want this behavior and always want the same duration regardless of the current value of the easer, don't specify a from value.

Interupting easings in progress: if start-easing! is called on an easer that is already in an easing transition that hasn't completed, it is equivalent to cancelling the current easing and sending the easer in a different direction starting from the current value. If there was on on-complete callback to the easing that was in progress it won't be called and is effectively "cancelled".

Cursors

cursor's in freactive behave and look exactly like atom's. You can use Clojurescript's built-in swap! and reset! functions on them and state will be propogated back to their parents. By default, change notifications from the parent propagate to the cursor when and only when they affect the state of the cursor.

cursors can be created by passing in a path that would be passed to get-in or assoc-in to the cursor function:

(cursor my-atom [:a :b 0])

Fundamentally, however, cursors are based on lenses! That means that you can pass any arbitrary getter (of the form (fn [parent-state])) and setter (of the form (fn [parent-state cursor-state])) and the cursor will handle it.

Items View

TODO

Configuration of Change Notifications