js-on-sx: Object.keys throws on null/undefined, walks indices on string/array

lib/js/runtime.sx

@@ -3982,6 +3982,18 @@
   (fn
     (o)
     (cond
+      ((or (= o nil) (js-undefined? o))
+        (raise (js-new-call TypeError (js-args "Object.keys called on null or undefined"))))
+      ((= (type-of o) "string")
+        (let ((result (list)) (n (len o)))
+          (begin
+            (js-string-keys-loop result 0 n)
+            result)))
+      ((list? o)
+        (let ((result (list)) (n (len o)))
+          (begin
+            (js-string-keys-loop result 0 n)
+            result)))
       ((dict? o)
         (cond
           ((contains? (keys o) "__js_order__")
@@ -4002,6 +4014,17 @@
                 result)))))
       (else (list)))))
 
+(define
+  js-string-keys-loop
+  (fn
+    (acc i n)
+    (cond
+      ((>= i n) nil)
+      (else
+        (begin
+          (append! acc (js-to-string i))
+          (js-string-keys-loop acc (+ i 1) n))))))
+
 (define
   js-object-values
   (fn