js-on-sx: for-in walks proto chain with shadowing, stops at native prototypes

lib/js/runtime.sx

@@ -3844,6 +3844,42 @@
     (k)
     (or (= k "__js_order__") (= k "__proto__"))))
 
+(define
+  js-for-in-keys
+  (fn
+    (o)
+    (let
+      ((result (list)))
+      (begin (js-for-in-walk o result) result))))
+
+(define
+  js-for-in-walk
+  (fn
+    (o acc)
+    (cond
+      ((not (dict? o)) nil)
+      ((= o (get Object "prototype")) nil)
+      ((= o (get Array "prototype")) nil)
+      ((= o (get Number "prototype")) nil)
+      ((= o (get String "prototype")) nil)
+      ((= o (get Boolean "prototype")) nil)
+      ((= o (get Date "prototype")) nil)
+      ((= o (get RegExp "prototype")) nil)
+      ((= o (get Map "prototype")) nil)
+      ((= o (get Set "prototype")) nil)
+      ((= o (get js-function-global "prototype")) nil)
+      (else
+        (let
+          ((own (js-object-keys o)))
+          (begin
+            (for-each
+              (fn (k) (if (contains? acc k) nil (append! acc k)))
+              own)
+            (cond
+              ((contains? (keys o) "__proto__")
+                (js-for-in-walk (get o "__proto__") acc))
+              (else nil))))))))
+
 (define
   js-object-keys
   (fn