CIDER, how to fix "No cljs REPLs in current session" error

Question

I'm editing a ClojureScript file, and I have a working ClojureScript REPL in another buffer. But when I try to evaluate a form in my file ui.cljs, with C-c C-c, I get a beep an a message in the mini-buffer that says

No cljs REPLs in current session "MyProjectDir/MyProject:localhost:59437

I don't really understand what that means, but it appears that my ui.cljs file got associated with the wrong REPL - the Clojure REPL, not the CLJS REPL.

CIDER Sessions:

1: MyProjectDir/MyProject:localhost:59437  
    linked-to: buf(ui.cljs)  
      objects: *cider-repl %s(clj)*  

2: MyProjectDir/MyProject:localhost:60016
    linked-to: >proj(~/Workspace/MyProjectDir/MyProject/)  
      objects: *cider-repl %s(cljs:weasel)*  

I try to "unlink" it by running the sesman-unlink command in the ui.cljs buffer. But I only get a beep and a cryptic error message in the minibuffer:

Wrong type argument: stringp, #<buffer ui.cljs>

How to associate that ui.cljs file/buffer with the correct REPL?

Emacs 25.3.1 on macOS. CIDER 0.19.0

Answer 1

There is a detailed comparison of the different cljs repls to date in lambdaisland

Borrowing from this rich and reputable source here is the bits of code you need to have configured for running weasel:

Server (Clojure)

(cljs.repl/repl (weasel.repl.websocket/repl-env :ip "0.0.0.0" :port 9001))

Client (ClojureScript)

(ns main
  (:require [weasel.repl :as repl]))

(when-not (repl/alive?)
  (repl/connect "ws://localhost:9001"))

I do recommend using figwheel repl. Here is a video (also by Arne of LambdaIsland) going through the configuration for Figwheel with Cider: link to youtube

Alternatively shadow-cljs is a different approach complete solution that's easy to configure, repl and all.