js-on-sx: split(undefined) returns whole string, funcexpr implicit return is undefined

lib/js/runtime.sx

@@ -2969,14 +2969,19 @@
           (&rest args)
           (let
             ((sep (if (= (len args) 0) :js-undefined (nth args 0)))
-              (limit
-                (if
-                  (< (len args) 2)
-                  -1
-                  (js-num-to-int (nth args 1)))))
+              (limit-raw (if (< (len args) 2) :js-undefined (nth args 1))))
             (let
-              ((result (js-string-split s (js-to-string sep))))
-              (if (< limit 0) result (js-list-take result limit))))))
+              ((limit
+                 (cond
+                   ((js-undefined? limit-raw) -1)
+                   (else (js-num-to-int (js-to-number limit-raw))))))
+              (cond
+                ((js-undefined? sep) (js-make-list s))
+                ((= limit 0) (js-make-list))
+                (else
+                  (let
+                    ((result (js-string-split s (js-to-string sep))))
+                    (if (< limit 0) result (js-list-take result limit)))))))))
       ((= name "concat")
         (fn (&rest args) (js-string-concat-loop s args 0)))
       ((= name "includes")

lib/js/transpile.sx

@@ -1503,7 +1503,7 @@
                   (list
                     (js-sym "fn")
                     (list (js-sym "__return__"))
-                    (cons (js-sym "begin") (append inits body-forms))))))
+                    (cons (js-sym "begin") (append (append inits body-forms) (list nil)))))))
             (list
               (js-sym "if")
               (list (js-sym "=") (js-sym "__r__") nil)