js4clj is a library aiming for facilitating the interop between Clojure and JavaScript on JVM using GraalVM and GraalJS.

Prerequisite & Installation

TODO

Usage

Requiring Namespaces

(ns net.coruscation.js4clj.example
  (:require
   [net.coruscation.js4clj.require :refer [require-js]]
   [net.coruscation.js4clj.utils :refer [js. js.- js.. clj->js js->clj js-set!]]
   [net.coruscation.js4clj.core :refer [js-new]]
   [net.coruscation.js4clj.js :as js]))

Using JavaScript Libraries

Install JavaScript libraries in the project root using npm like usual.

npm init
npm i luxon # luxon as an example

;; we can use luxon as a namespace now, for example: luxon/DateTime
(require-js '["luxon" :as luxon])

Converting data between Clojure and JavaScript

This library provides two functions similar to those of ClojureScript: js->clj and clj->js.

;; result: #object[org.graalvm.polyglot.Value 0x22b60c71 "{key: \"value\"}"]
(def js-obj (clj->js {:key "value"}))
;; result: {:key "value"}
(js->clj js-obj :keywordize-keys true) 

Calling JavaScript functions, get/set JavaScript properties

Similar to ClojureScript, this libraries provides four macros: js. js.- js.. and js-set!

We can use js. to call a method of an Object.

(def current-time (js. luxon/DateTime now))
;; result: "2025-11-27T23:27:34.853+08:00"
(js. current-time toString) 

We can use js.- to access properties of an object.

;; result: "value"
(js.- (clj->js {:key "value"})
	  key) 

We can also use js.. to chain the calling

(js.. luxon/DateTime now toString)

We can also use js.. to access property by using - as a prefix:

(js.. luxon/DateTime
  (fromObject (clj->js {:day 22}))
  (plus (clj->js {:day 1}))
  ;; results: 23
  -day) 

The library also provides a js-set!, it must be used along with js.- or js...

(let [obj (clj->js {})]
  (js-set! (js.- obj key)
           "value")

  (js.- obj key) ;; "value"

  (js-set! (js.. obj -key)
           "new value")
  (js.- obj key) ;; "new value"
  )

Examples

You can check this minimal Server Side Rendering with Client Side Rehydration example using react.

Links

This project is inspired by:

• libpython-clj
• py4clj

Check this blog about roughly how it is done Experiment with GraalVM, Clojure, and JavaScript.