ClojureScript

CIDER works with ClojureScript, but you should keep in mind that not all the functionality available with Clojure exists for ClojureScript (at least not yet). To give you a concrete example - things like running tests and the debugger are currently Clojure-only features.

ClojureScript support relies on the piggieback nREPL middleware being present in your REPL session. There's one exception to this, though - shadow-cljs. It has its own nREPL middleware and doesn't rely on piggieback at all.

To setup piggieback add the following dependencies to your project (project.clj in Leiningen based project or build.boot in Boot project):

;; use whatever are the most recent versions here
[cider/piggieback "0.3.2"]
[org.clojure/clojure "1.9.0"]

as well as piggieback nREPL middleware:

in project.clj:

:repl-options {:nrepl-middleware [cider.piggieback/wrap-cljs-repl]}

or in build.boot:

(task-options!
  repl {:middleware '[cider.piggieback/wrap-cljs-repl]})

There are many ClojureScript REPLs out there and it's often hard to wrap your head around them and the differences between them. You'd do well to read this awesome article before proceeding with the rest of the instructions listed here.

Open a file in your project and issue M-x cider-jack-in-clojurescript RET. This will start up the nREPL server, and then create two REPL buffers for you, one in Clojure and one in ClojureScript. All usual CIDER commands will be automatically directed to the appropriate REPL, depending on whether you're visiting a .clj or a .cljs file.

cider-jack-in-clojurescript will prompt you about the type of ClojureScript to start. Keep in mind that some of the REPLs will require some additional setup, before you can make use of them (e.g. you'll need to have Node.js installed to be able to start a node REPL).

You can suppress the prompt the REPL to use by setting cider-default-cljs-repl. Here's an example that will make Nashorn the default:

(setq cider-default-cljs-repl 'nashorn)

All supported ClojureScript REPLs are stored in cider-cljs-repl-types. If you need to extend it, you should use cider-register-cljs-repl-type in your Emacs configuration.

(cider-register-cljs-repl-type 'super-cljs "(do (...))" optional-requirements-function)

You can also create a ClojureScript REPL with the command cider-create-sibling-cljs-repl in cases where you already have a Clojure REPL running.

Continue reading for the additional setup needed for the various ClojureScript REPLs out there.

Browser-connected ClojureScript REPL

Using Weasel, you can also have a browser-connected REPL.

  1. Add [weasel "0.7.0"] to your project's :dependencies.

  2. Issue M-x cider-jack-in-clojurescript RET and choose the Weasel option when prompted about the ClojureScript REPL type you want to use.

  3. Add this to your ClojureScript code:

(ns my.cljs.core
  (:require [weasel.repl :as repl]))
(repl/connect "ws://localhost:9001")
  1. Open a file in your project and issue M-x cider-jack-in-clojurescript.

Provided that a Piggieback-enabled ClojureScript environment is active in your REPL session, code loading and evaluation will work seamlessly regardless of the presence of the cider-nrepl middleware. If the middleware is present then most other features of CIDER will also be enabled (including code completion, documentation lookup, the namespace browser, and macroexpansion).

Browser-connected ClojureScript REPL in Boot project

  1. Add this to your dependencies in build.boot:
[adzerk/boot-cljs        "X.Y.Z"  :scope "test"]
[adzerk/boot-cljs-repl   "X.Y.Z"  :scope "test"]
[pandeiro/boot-http      "X.Y.Z"  :scope "test"]
[weasel                  "0.7.0"  :scope "test"]
[cider/piggieback "0.3.2"  :scope "test"]

and this at the end of build.boot:

(require
 '[adzerk.boot-cljs :refer [cljs]]
 '[adzerk.boot-cljs-repl :refer [cljs-repl]]
 '[pandeiro.boot-http :refer [serve]])

(deftask dev []
  (comp (serve)
        (watch)
        (cljs-repl) ; order is important!!
        (cljs)))

  1. Issue M-x customize-variable RET cider-boot-parameters and insert dev.

  2. Open a file in your project and issue M-x cider-jack-in-clojurescript.

  3. Connect to the running server with your browser. The address is printed on the terminal, but it's probably http://localhost:3000.

For more information visit boot-cljs-repl.

Using the Figwheel REPL (Leiningen-only)

You can also use Figwheel with CIDER.

  1. Set up Figwheel as normal, but make sure :cljsbuild and :figwheel settings are in the root of your Leiningen project definition.

  2. Add these to your dev :dependencies:

[cider/piggieback "0.3.2"]
[figwheel-sidecar "0.5.16"] ; use here whatever the current version of figwheel is

Keep in mind that figwheel 0.5.16 is the first to support piggieback 0.3. If you're using an older figwheel you should stick to piggieback 0.2.2 (which uses the old com.cemerick/piggieback package coordinates).

  1. Add this to your dev :repl-options:
:nrepl-middleware [cider.piggieback/wrap-cljs-repl]

  1. Start the REPL with cider-jack-in-clojurescript (C-c M-J)

  2. Open a browser to the Figwheel URL so that it can connect to your application.

You now have two nREPL connections, one for Clojure and one for ClojureScript. CIDER will determine which to use based on the type of file you're editing.

You should also check out Figwheel's wiki.

Using shadow-cljs

Provided you've configured your project correctly you can simply use cider-jack-in-clojurescript to use shadow-cljs.

This will automatically start the shadow-cljs server and connect to it. You'll also be prompted for the build to use.

Alternatively you can start the server manually with something like:

npx shadow-cljs server

And connect to it with cider-connect.

Working with .cljc files

Ordinarily, CIDER dispatches code from clj files to Clojure REPLs and cljs files to ClojureScript REPLs. However, cljc files have two possible connection targets. By default, CIDER tries to evaluate cljc files in all matching connection buffers, both clj and cljs (if present).

Simply put - if you're evaluating the code (+ 2 2) in a cljc file and you have an active Clojure and and active ClojureScript REPL, then the code is going to be evaluated 2 times - once for each of them. This behavior might be a bit confusing, but that's what we came up with, when ruminating what was the most logical thing to do out-of-the-box.

This can be modified with M-x cider-toggle-connection-buffer RET. Toggling this once will choose one of the connections as the primary, and successive calls to M-x cider-toggle-connection-buffer RET will alternate which connection to use. To restore evaluation to both connections, invoke cider-toggle-connection-buffer with a prefix argument (C-u M-x cider-toggle-connection-buffer RET).

If there is only a Clojure connection, no toggling will happen and a message will inform you that there are no other connections to switch to.