An easy to use, decomplected hiccup compiler for ClojureScript & React.

clj, clojurescript, hiccup, react, react-components



Clojars Project

A simple, easy to use library for React development in ClojureScript.

(ns my-app.core
  (:require [hx.react :as hx]
            ["react-dom" :as react-dom]))

(hx/defnc MyComponent [{:keys [name]}]
  [:div "Hello " 
   [:span {:style {:font-weight "bold"}} name] "!"])

  (hx/f [MyComponent {:name "React in CLJS"}])
  (. js/document getElementById "app"))


You'll want to make sure you have the latest version of react, react-is, and whatever renderer you are targeting (e.g. react-dom).

npm i react react-is react-dom

If you want to use the React Hooks API (hx.react.hooks), you'll need to install the 16.7.0-alpha version:

npm i react@next react-dom@next react-is

Project status

  • Hiccup interpreter

The hiccup interpreter is done other than bugs AFAICT. Please open any issues you find with using components in hiccup forms.

  • def<thing> helper macros

The helper macros are pretty much done, but are subject to change as they are used in anger and either limitations or potential improvements are found.

  • React Hooks enhancements

React Hooks is a new proposal for a way of representing state and other side effects as function calls and data, removing the need for functional components.

These will work out of the box with hx, but there are some improvements to be made (IMO) to make them even more ergonomic for developers.

  • CLJ support

Support for interpretation of hiccup and definition of components in JVM Clojure.

What problems does hx solve?

hx is meant to make it simple, easy and fun to use React.js within ClojureScript. It is your bridge to the wide world of React.js in idiomatic CLJS.

The library is split into (currently) two sections, which you can feel free to mix as your project sees fit:

  1. A hiccup interpreter. Takes in [:div {:style {:color "red"}} [:span "foo"]] and spits out React.createElement calls.

  2. Helpers for creating components. defnc and defcomponent help us write plain React.js components in idiomatic ClojureScript.

What's hiccup?

TL;DR: hiccup is the JSX of the Clojure ecosystem

hx.hiccup is an implementation of a "hiccup" syntax interpreter. Hiccup is a way of representing HTML using clojure data structures. It uses vectors to represent elements, and maps to represent an elements attributes.

The original hiccup library was written for Clojure and outputs HTML strings. This library is written for use in CLJS and outputs React data structures. It extends the syntax slightly to accomodate using any arbitrary React component in place of HTML tags.

The basis of the library is the parse function that takes in a hiccup form and transforms it into calls to React's createElement function:

(require '[hx.hiccup :as hiccup])

  [ReactComponent {:some-prop #js {:foo "bar"}}
   [:div {:class "greeting"} "Hello, ReactJS!"]])
;; executes:
;;    (react/createElement ReactComponent #js {:some-prop #js {:foo "bar"}}
;;      (react/createElement #js {:className "greeting"}
;;        "Hello, ReactJS!"))

The hiccup parser can be extended with custom tags by defining a new hx.hiccup/parse-element method. For example, here's how we handle :<> for fragments:

(defmethod hiccup/parse-element :<>
  [el & args]

What problems does hx not solve?

No opinionated state management, no custom rendering queue. Use it to build your awesome opinionated async reactive immutable app framework. hx is just a Clojure-y interface to creating plain, unadulterated React components.

Authoring components

hx doesn't do anything special in regards to how it calls or creates React components. They are assumed to act like native, vanilla React components that could be used in any codebase.

In practice, this is fairly easy to handle in ClojureScript. A basic functional component can be written as just a normal function that returns a React element:

(defn MyComponent [props]
  (hiccup/parse [:div "Hello"]))
(react-dom/render (hiccup/parse [MyComponent]) (. js/document getElementById "app"))

props will always be a JS object, so if we want to pull something out of it, we'll need to use JS interop:

(defn MyComponent [props]
  (let [name (goog.object/get props "name")]
    (hiccup/parse [:div "Hello, " name "!"]))
(react-dom/render (hiccup/parse [MyComponent {:name "Uma"}])
                  (. js/document getElementById "app"))

hx.react/defnc is a macro that shallowly converts the props object for us and wraps our function body in hiccup/parse, so we can get rid of some of the boilerplate:

(hx/defnc MyComponent [{:keys [name]}]
  [:div "Hello, " name "!"])

Children are also passed in just like any other prop, so if we want to obtain children we simply peel it off of the props object:

(defn HasChildren [props]
  (let [children (goog.object/get props "children")]
       {:style {:border "1px solid #000"}}

;; or
(hx/defnc HasChildren [{:keys [children]}]
   {:style {:border "1px solid #000"}}

Sometimes we also need access to React's various lifecycle methods like componentDidMount, componentDidUpdate, etc. In that case, we should create a React component class. hx exposes a very barebones hx/defcomponent macro that binds closely to the OOP, class-based API React has for maximum flexibility. You can also leverage libraries like Om.Next, Reagent, Rum, or other frameworks that have state management built in.

Hiccup forms & interpreter behavior

hx.hiccup makes several default decisions about how hiccup and components should be written.

For a number of examples, check out the workshop in the examples folder.

Writing hiccup

First, all hiccup forms are assumed to follow the same pattern:

[ <(1)elementType> <(2)props-map?> <(3)child> ... <(n)child> ].

The element in the (1) first position are assumed to be valid React element types. They can be:

  1. A keyword that maps to a native element - such as :div, :span, :nav. These are mapped to a string and passed into createElement.

  2. A function that returns React elements, aka a functional component.

  3. An object that extends the React.Component class.

  4. One of the built-in React symbols, such as React.Fragment, a context provider, context consumer, etc.

Regardless of the type of the element in position (1), if you want to pass in props to a component, they are always passed in via a map in the (2) second position. Props can be written as a map literally or a symbol bound to a map. If the element in position (2) is not a map, it is assumed to be a child and passed into the children field of createElement.

Finally, anything passed into position (3) or on is considered a child element.

Here are a few examples. hx.react/defnc is used for concision, the only thing it does is coerce props to a map and wrap the body in a call to hiccup/parse:

;;  has children, but no props. Strings are considered valid children.
(hx/defnc Greet [_]
  [:div "Hello"])

;; component that is passed in a map of props
(hx/defnc MediumGreet [_]
  [:div {:style {:font-size "28px"}} "Medium hello"])

;; binding props and children to symbols and passing it into the element.
(hx/defnc BigGreet [_]
    (let [props {:style {:font-size "56px"}}
          children "Big hello"]
      [:div props children]))

;; passing in multiple children, and calling components that we defined ourselves
;; (instead of native elements like `:div`).
(hx/defnc AllGreets []

;; sequences are wrapped in react Fragments for ease of use
(hx/defnc Sequence []
   (for [color ["red" "green" "blue"]]
     ;; add a key prop to help React
     [:strong {:style {:color color} :key color} color])])
;; using children as a function
(hx/defnc FnAsChild [{:keys [children]}]
  [:div (children "foo")])

;; passing in children as a function
(hx/defnc UseFnAsChild [_]
  [FnAsChild (fn [value]
                [:h1 value])])

hx.hiccup shallowly converts props to a JS object at runtime. Your kebab-case props will be converted to camelCase before passed into a native element. :style is special-cased to recursively convert to a JS obj to help with using native elements as well.

Top-level API

If all you want is the hiccup interpreter, you may simple import hx.hiccup:

(require '[hx.hiccup :as hiccup])

(hiccup/parse [:div "foo"]) ;; => {$$typeof: Symbol(react.element), type: "div", key: null, ref: null, props: {…}, …}


hx.react contains a number of helpful functions and macros for doing React development in ClojureScript.

hx.react/f ([form])

An alias of hx.hiccup/parse, so that if you need to do some ad-hoc transformation of hiccup one doesn't have to import hx.hiccup as well as hx.react.

hx.react/defnc: ([name props-bindings & body])

This macro is just like defn, but shallowly converts the props object passed in to the component to a Clojure map and intelligently interprets the return value of the body as hiccup. If the body doesn't return a vector, it simply returns that value.

Takes a name, props bindings and a function body.

Example usage:

(require '[hx.react :as hx])
(require '[hx.hiccup])

(hx/defnc Greeting [{:keys [name] :as props}]
  [:span {:style {:font-size "24px"}}
   "Hello, " name "!"])

  (hx.hiccup/parse [Greeting {:name "Tara"}])
  (. js/document getElementById "app"))

hx.react/defcomponent: ([name constructor & body])

This macro creates a React component class. Is the CLJS equivalent of class {name} extends React.Component { ... . constructor is passed in this and must return it. Additional methods and static properties can be passed in, similar to defrecord / deftype. Methods are automatically bound to this.

Example usage:

(hx/defcomponent MyComponent
  (constructor [this]
    (set! (. this -state) #js {:name "Maria"})

  (greeting "Hello")
  (update-name! [this e]
    (. this setState #js {:name (.. e -target -value)}))

  (render [this]
    (let [state (. this -state)]
       [:div (. my-component -greeting) ", " (. state -name)]
       [:input {:value (. state -name)
                :on-change (. this -update-name!)}]])))

hx.react/$: ([el p & c])

An alias for react/createElement. It will marshall props from a map to JS and interpret any hiccup children.

hx.react/factory: ([component])

Creates a factory function from a component (e.g. a function, class, or string) that, when called, returns a React element.

hx.react/shallow-render: ([& body])

Short-circuits the hiccup interpreter to return just the hiccup form returned by body. Very useful for testing React components created using hx.hiccup.


(hx/defnc Welcome [{:keys [age]}]
  (if (> age 17))
    [:div "You're allowed!"]
    [:div [:a {:href ""}] "Please go elsewhere"])
;; in test
(deftest welcome-allowed
  (is (= (hx/shallow-render (Welcome {:keys age}))
         [:div "You're allowed!"]))
  (is (= (hx/shallow-render (Welcome {:age 17}))
         [:div [:a {:href ""}] "Please go elsewhere"])))


Copyright © 2018 Will Acton

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