js-on-sx: getOwnPropertyDescriptor handles arrays + strings

lib/js/runtime.sx

@@ -4042,10 +4042,36 @@
   js-object-get-own-property-descriptor
   (fn
     (o key)
-    (if
-      (and (dict? o) (contains? (keys o) (js-to-string key)))
-      {:configurable true :enumerable true :value (get o (js-to-string key)) :writable true}
-      :js-undefined)))
+    (let
+      ((sk (js-to-string key)))
+      (cond
+        ((and (dict? o) (contains? (keys o) sk))
+          {:configurable true :enumerable true :value (get o sk) :writable true})
+        ((list? o)
+          (cond
+            ((= sk "length")
+              {:configurable false :enumerable false :value (len o) :writable true})
+            ((js-int-key? sk)
+              (let
+                ((i (js-num-to-int (js-string-to-number sk))))
+                (cond
+                  ((and (>= i 0) (< i (len o)))
+                    {:configurable true :enumerable true :value (nth o i) :writable true})
+                  (else :js-undefined))))
+            (else :js-undefined)))
+        ((and (= (type-of o) "string"))
+          (cond
+            ((= sk "length")
+              {:configurable false :enumerable false :value (len o) :writable false})
+            ((js-int-key? sk)
+              (let
+                ((i (js-num-to-int (js-string-to-number sk))))
+                (cond
+                  ((and (>= i 0) (< i (len o)))
+                    {:configurable false :enumerable true :value (char-at o i) :writable false})
+                  (else :js-undefined))))
+            (else :js-undefined)))
+        (else :js-undefined)))))
 
 (define
   js-object-get-own-property-descriptors