reagent

by reagent-project

reagent-project / reagent

A minimalistic ClojureScript interface to React.js

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Reagent

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A simple ClojureScript interface to React.

Reagent provides a way to write efficient React components using (almost) nothing but plain ClojureScript functions.

Usage

To create a new Reagent project using Leiningen template simply run:

lein new reagent myproject

If you wish to only create the assets for ClojureScript without a Clojure backend then do the following instead:

lein new reagent-frontend myproject

This will setup a new Reagent project with some reasonable defaults, see here for more details.

To use Reagent in an existing project you add this to your dependencies in

project.clj
:

Clojars Project

This is all you need to do if you want the standard version of React. If you want to use your own build of React (or React from a CDN), you have to use

:exclusions
variant of the dependency, and also provide
react
and
react-dom
namespaces (by creating
.cljs
files with just
ns
form, or by adding your own
:foreign-libs
entries).
[reagent "0.x.x" :exclusions [cljsjs/react cljsjs/react-dom]]

Examples

Reagent uses Hiccup-like markup instead of React's sort-of html. It looks like this:

(defn some-component []
  [:div
   [:h3 "I am a component!"]
   [:p.someclass
    "I have " [:strong "bold"]
    [:span {:style {:color "red"}} " and red"]
    " text."]])

Reagent extends standard Hiccup in one way: it is possible to "squeeze" elements together by using a

>
character.
[:div
  [:p
    [:b "Nested Element"]]]

can be written as:

[:div>p>b "Nested Element"]

Since version 0.8: The

:class
attribute also supports collections of classes, and nil values are removed:
[:div {:class ["a-class" (when active? "active") "b-class"]}]

You can use one component inside another:

(defn calling-component []
  [:div "Parent component"
   [some-component]])

And pass properties from one component to another:

(defn child [name]
  [:p "Hi, I am " name])

(defn childcaller [] [child "Foo Bar"])

You mount the component into the DOM like this:

(defn mountit []
  (rd/render [childcaller]
            (.-body js/document)))

assuming we have imported Reagent like this:

(ns example
  (:require [reagent.core :as r]
            [reagent.dom :as rd]))

State is handled using Reagent's version of

atom
, like this:
(defonce click-count (r/atom 0))

(defn state-ful-with-atom [] [:div {:on-click #(swap! click-count inc)} "I have been clicked " @click-count " times."])

Any component that dereferences a

reagent.core/atom
will be automatically re-rendered.

If you want to do some setting up when the component is first created, the component function can return a new function that will be called to do the actual rendering:

(defn timer-component []
  (let [seconds-elapsed (r/atom 0)]
    (fn []
      (js/setTimeout #(swap! seconds-elapsed inc) 1000)
      [:div
       "Seconds Elapsed: " @seconds-elapsed])))

This way you can avoid using React's lifecycle callbacks like

getInitialState
and
componentWillMount
most of the time.

But you can still use them if you want to, either using

reagent.core/create-class
or by attaching meta-data to a component function:
(defonce my-html (r/atom ""))

(defn plain-component [] [:p "My html is " @my-html])

(def component-with-callback (with-meta plain-component {:component-did-mount (fn [this] (reset! my-html (.-innerHTML (reagent/dom-node this))))}))

See the examples directory for more examples.

Performance

React is pretty darn fast, and so is Reagent. It should even be faster than plain old javascript React a lot of the time, since ClojureScript allows us to skip a lot of unnecessary rendering (through judicious use of React's

shouldComponentUpdate
).

The ClojureScript overhead is kept down, thanks to lots of caching.

Code size is a little bigger than React.js, but still quite small. The todomvc example clocks in at roughly 79K gzipped, using advanced compilation.

About

The idea and some of the code for making components atom-like comes from pump. The reactive-atom idea (and some code) comes from reflex.

The license is MIT.

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