Weasel uses WebSockets to communicate between a ClojureScript REPL, which is typically hosted on nREPL using piggieback, and an environment which can execute compiled ClojureScript, which can be a web browser or any JavaScript environment that supports the WebSocket APIs.
We're looking for more maintainers for the project. If you're interested in helping out please ping @bbatsov.
- A WebSocket transport is simple and avoids some of the thornier bugs
caused by the
CrossPageChanneltransport, which is used in the standard ClojureScript browser REPL and Austin. (see: cemerick/austin#17, cemerick/austin#47, cemerick/austin#49) - WebSocket APIs are available far beyond the browser - Node, Deno, Bun, web and service workers, browser extensions, React Native, and more exotic embeddings like QML - so Weasel can give you a REPL driven workflow in environments where the iframe-based standard browser REPL simply can't run.
Weasel is intended to be used with nREPL's
piggieback middleware. Once you've set that up,
add Weasel as a dependency to project.clj:
[weasel "0.7.1" :exclusions [org.clojure/clojurescript]]Or, if you're using deps.edn:
{:deps {weasel/weasel {:mvn/version "0.7.1"}}}Start up lein repl and piggieback the Weasel REPL environment onto
the nREPL session, optionally specifying a port (defaults to 9001) and
an address to bind to (defaults to "127.0.0.1").
user> (require 'weasel.repl.websocket)
nil
user> (cider.piggieback/cljs-repl
(weasel.repl.websocket/repl-env :ip "0.0.0.0" :port 9001))
<< started Weasel server on ws://127.0.0.1:9001 >>
<< waiting for client to connect ...Weasel will block the REPL, waiting for a client to connect.
In your project's ClojureScript source, require the Weasel client namespace and connect to the REPL.
(ns my.cljs.core
(:require [weasel.repl :as repl]))
(when-not (repl/alive?)
(repl/connect "ws://localhost:9001"))You may optionally specify the following:
:verbose ; boolean, defaults to true
:print ; :repl to print only to the repl,
; :console to print only to the console
; #{:repl :console} to print to both
; or any variadic function to handle printing differently.
; defaults to :repl
:on-open, :on-error, :on-close ; fns for handling websocket lifecycle events.
; default for all is nil. :on-open and :on-close
; fire once per connection (not on every
; reconnect); :on-error receives the native
; WebSocket event.
:reconnect? ; boolean, whether to reconnect automatically when the
; connection drops. defaults to true
:reconnect-delay ; initial reconnect backoff in ms, defaults to 1000.
; the delay doubles after each failed attempt
:max-reconnect-delay ; ceiling for the backoff in ms, defaults to 30000
:heartbeat-interval ; ms between keepalive pings used to detect a silently
; dead connection. 0 disables it, which is the default.
; a few missed pongs are tolerated before the link is
; considered dead, and a server that never answers pings
; is left undisturbedThe connection survives page reloads and server restarts on its own, retrying
with the backoff until it gets back in (or the server rejects it outright, e.g.
when another client already holds the REPL). Call (repl/disconnect) to close
it for good and stop the reconnection attempts.
Connecting with options:
(repl/connect "ws://localhost:9001"
:verbose true
:print #{:repl :console}
:on-error #(print "Error! " %))Load the script in your WebSocket-enabled environment (probably a page in a web browser) and start evaluating ClojureScript at the REPL:
cljs.user> (= (js/Number. 34) (js/Number. 34))
false
cljs.user> (do (js/alert "Hello world!") 42)
42Because the client talks over the platform's native WebSocket, it isn't tied
to the browser. Any runtime with a global WebSocket works, including Node 22+,
Deno, Bun, and web/service workers. Require weasel.repl from code compiled for
that target and call repl/connect exactly as you would in a browser:
(ns my.app
(:require [weasel.repl :as repl]))
(repl/connect "ws://localhost:9001")The only browser-specific piece is Closure's script-tag code loading used to
pull in namespaces first required at the REPL; it's skipped automatically when
there is no document. Evaluating forms, printing, reconnection and the
heartbeat all behave the same everywhere.
Note that unless a client is connected to the WebSocket channel, evaluation will fail:
cljs.user> (+ 5 10)
java.io.IOException: No client connected to Websocket
nilOnly a single client can be connected to the REPL at once. Attempting to connect to an occupied REPL server will throw an exception in the client.
An example project is included in the weasel-example subdirectory of
this project.
If you have any feedback or issues to report, feel free to open an issue on GitHub.
A little treat for reading the whole README!
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means.
In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to http://unlicense.org/.