## 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.


### Piggieback

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.

If `cider-inject-dependencies-at-jack-in` is enabled (which is the default) then
piggieback will be automatically added and configured for your project when
doing `cider-jack-in-cljs`.

If this configuration option is disabled or you're going to connect to
an already running nREPL server using `cider-connect-cljs` - continue
reading ahead.

#### Manual Piggieback Setup

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

```clojure
;; use whatever are the most recent versions here
[cider/piggieback "0.3.9"]
[org.clojure/clojure "1.9.0"]
```

as well as `piggieback` nREPL middleware:

in `project.clj`:

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

or in `build.boot`:

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

### Starting a ClojureScript 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](https://lambdaisland.com/guides/clojure-repls/clojurescript-repls)
before proceeding with the rest of the instructions listed here.

Open a file in your project and issue <kbd>M-x</kbd>
`cider-jack-in-cljs` <kbd>RET</kbd>. This will start up the nREPL
server, and then create a ClojureScript REPL buffer for you, one.

!!! Note

    Prior to CIDER 0.18, `cider-jack-in-cljs` would create both a Clojure and
    a ClojureScript REPL. In CIDER 0.18+ if you want to create both REPLs
    you'll have to use `cider-jack-in-clj&cljs` instead.

When you have a combination of Clojure and ClojureScript REPLs 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-cljs` 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:

```el
(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.

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

You can also modify the known ClojureScript REPLs on a per-project basis using
`.dir-locals.el`:

```el
;; replace the list of REPLs types and set some default
((nil
  (cider-default-cljs-repl . super-cljs)
  (cider-cljs-repl-types . ((super-cljs "(do (foo) (bar))")))))
```

```el
;; modify the list of known REPLs and set some default
((nil
  (eval . (cider-register-cljs-repl-type 'super-cljs "(do (foo) (bar))"))
  (cider-default-cljs-repl . super-cljs)))
```

You can also create a ClojureScript REPL with the command
`cider-jack-in-sibling-clojurescript` 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 <kbd>M-x</kbd> `cider-jack-in-cljs` <kbd>RET</kbd> and choose
   the `Weasel` option when prompted about the ClojureScript REPL type you want
   to use.

3. Add this to your ClojureScript code:

```clojure
(ns my.cljs.core
  (:require [weasel.repl :as repl]))
(repl/connect "ws://localhost:9001")
```

4. Open a file in your project and issue <kbd>M-x</kbd> `cider-jack-in-cljs`.

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`:

```clojure
[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 "0.3.9"  :scope "test"] ; not needed for cider-jack-in-cljs
```

and this at the end of `build.boot`:

```clojure
(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)))
```

2. Issue <kbd>M-x</kbd> `customize-variable` <kbd>RET</kbd> `cider-boot-parameters`
   and insert `dev`.

3. Open a file in your project and issue <kbd>M-x</kbd> `cider-jack-in-cljs`.

5. 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](https://github.com/adzerk-oss/boot-cljs-repl).

### Using Figwheel (Leiningen-only)

!!! Warning

    This has been deprecated in favour of using `figwheel-main`. Check out
    the instructions in the next section.

You can also use [Figwheel](https://github.com/bhauman/lein-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`:

```clojure
[cider/piggieback "0.3.9"] ; not needed for cider-jack-in-cljs
[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).

3. Add this to your dev `:repl-options` (not needed for `cider-jack-in-cljs`):

```clojure
:nrepl-middleware [cider.piggieback/wrap-cljs-repl]
```

4. Start the REPL with `cider-jack-in-cljs` (<kbd>C-c C-x (C-)j (C-)s</kbd>). Select
`figwheel` when prompted about the ClojureScript REPL type.

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

You should also check out
[Figwheel's wiki](https://github.com/bhauman/lein-figwheel/wiki/Using-the-Figwheel-REPL-within-NRepl).

### Using Figwheel-main

!!! Note

    The instructions here assume you're using Leiningen. Adapting them to your
    favourite build tool is up to you.

You can also use [Figwheel-main](https://github.com/bhauman/figwheel-main) with CIDER.

1. Add this to your dev `:dependencies`:

```clojure
[cider/piggieback "0.3.9"] ; not needed for cider-jack-in-cljs
```

2. Add this to your dev `:repl-options` (not needed for `cider-jack-in-cljs`):

```clojure
:nrepl-middleware [cider.piggieback/wrap-cljs-repl]
```

3. Start the REPL with `cider-jack-in-cljs` (<kbd>C-c C-x (C-)j (C-)s</kbd>). Select
`figwheel-main` when prompted about the ClojureScript REPL type.

4. Select the Figwheel build to run when prompted for it. (e.g. `:dev`).

### Using shadow-cljs

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

Lastly, if you already have a running server watching a build, for instance you
have already run `npx shadow-cljs watch :dev`, you can use the `shadow-select`
CLJS REPL and specify `:dev` when prompted.

[leiningen]: http://leiningen.org/
[boot]: http://boot-clj.com/
[piggieback]: https://github.com/nrepl/piggieback
[shadow-cljs]: https://github.com/thheller/shadow-cljs

## 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 twice - once for each of the REPLs.  In fact, you can create
multiple clj and cljs sibling connections (<kbd>C-c C-x C-s C-s/j</kbd>) within
Cider session and evaluation will be directed into all REPLs simultaneously. See
[Managing Connections](managing_connections.md) for more details.