Fix #926: support add-watch on CLJS vars (#927)

CHANGELOG.md

@@ -10,6 +10,10 @@ SCI is used in [babashka](https://github.com/babashka/babashka),
 [joyride](https://github.com/BetterThanTomorrow/joyride/) and many
 [other](https://github.com/babashka/sci#projects-using-sci) projects.
 
+## Unreleased
+
+- Fix [#926](https://github.com/babashka/sci/issues/926): Support `add-watch` on vars in CLJS
+
 ## 0.8.43 (2024-08-06)
 
 - Fix shadow-cljs warnings

src/sci/impl/vars.cljc

@@ -225,7 +225,7 @@
 (defn var-set [v val]
   (t/setVal v val))
 
-(defn unqualify-symbol 
+(defn unqualify-symbol
   "If sym is namespace-qualified, remove the namespace, else return sym"
   [sym]
   (if (qualified-symbol? sym)

src/sci/lang.cljc

@@ -188,10 +188,19 @@
                       (vars/with-writeable-var this meta
                         (set! watches (assoc watches key fn)))
                       this)
-            (removeWatch [this _]
+            (removeWatch [this key]
                          (vars/with-writeable-var this meta
                            (set! watches (dissoc watches key)))
-                         this)])
+                         this)]
+      :cljs [IWatchable
+            (-add-watch [this key fn]
+                        (vars/with-writeable-var this meta
+                          (set! watches (assoc watches key fn)))
+                        this)
+            (-remove-watch [this key]
+                           (vars/with-writeable-var this meta
+                             (set! watches (dissoc watches key)))
+                           this)])
   ;; #?(:cljs Fn) ;; In the real CLJS this is there... why?
   #?(:clj clojure.lang.IFn :cljs IFn)
   (#?(:clj invoke :cljs -invoke) [this]

test/sci/vars_test.cljc

@@ -256,8 +256,7 @@
   (is (true? (eval* "(def ^:dynamic *x*) (def ^:dynamic *y*)
     (binding [*x* *x* *y* *y*] (thread-bound? #'*x* #'*x*))"))))
 
-#?(:clj
-   (deftest add-watch-test
-     (is (str/starts-with?
-          (sci/with-out-str (sci/eval-string "(def x 1) (add-watch #'x :foo (fn [k r o n] (prn :o o :n n))) (alter-var-root #'x (constantly 5))"))
-          ":o 1 :n 5"))))
+(deftest add-watch-test
+  (is (str/starts-with?
+       (sci/with-out-str (sci/eval-string "(def x 1) (add-watch #'x :foo (fn [k r o n] (prn :o o :n n))) (alter-var-root #'x (constantly 5))"))
+       ":o 1 :n 5")))