diff --git a/lib/js/parser.sx b/lib/js/parser.sx
index 5b1d1bb7..4e88f2d4 100644
--- a/lib/js/parser.sx
+++ b/lib/js/parser.sx
@@ -418,17 +418,43 @@
               (dict-set! st :idx saved)
               (jp-advance! st)
               (let
-                ((e (jp-parse-assignment st)))
+                ((e (jp-parse-comma-seq st)))
                 (jp-expect! st "punct" ")")
                 e)))
           (do
             (dict-set! st :idx saved)
             (jp-advance! st)
             (let
-              ((e (jp-parse-assignment st)))
+              ((e (jp-parse-comma-seq st)))
               (jp-expect! st "punct" ")")
               e)))))))
 
+(define
+  jp-parse-comma-seq
+  (fn
+    (st)
+    (let
+      ((first-expr (jp-parse-assignment st)))
+      (if
+        (jp-at? st "punct" ",")
+        (jp-parse-comma-seq-rest st (list first-expr))
+        first-expr))))
+
+(define
+  jp-parse-comma-seq-rest
+  (fn
+    (st acc)
+    (do
+      (jp-advance! st)
+      (let
+        ((next-expr (jp-parse-assignment st)))
+        (let
+          ((acc2 (append acc (list next-expr))))
+          (if
+            (jp-at? st "punct" ",")
+            (jp-parse-comma-seq-rest st acc2)
+            (cons (quote js-comma) (list acc2))))))))
+
 (define
   jp-collect-params
   (fn
diff --git a/lib/js/test262-scoreboard.json b/lib/js/test262-scoreboard.json
index 9cadeee2..546be845 100644
--- a/lib/js/test262-scoreboard.json
+++ b/lib/js/test262-scoreboard.json
@@ -1,45 +1,37 @@
 {
   "totals": {
     "pass": 46,
-    "fail": 2,
+    "fail": 4,
     "skip": 0,
-    "timeout": 2,
+    "timeout": 0,
     "total": 50,
     "runnable": 50,
     "pass_rate": 92.0
   },
   "categories": [
     {
-      "category": "built-ins/Number",
+      "category": "built-ins/Object",
       "total": 50,
       "pass": 46,
-      "fail": 2,
+      "fail": 4,
       "skip": 0,
-      "timeout": 2,
+      "timeout": 0,
       "pass_rate": 92.0,
       "top_failures": [
         [
-          "Timeout",
-          2
-        ],
-        [
-          "Test262Error (assertion failed)",
-          2
+          "ReferenceError (undefined symbol)",
+          4
         ]
       ]
     }
   ],
   "top_failure_modes": [
     [
-      "Timeout",
-      2
-    ],
-    [
-      "Test262Error (assertion failed)",
-      2
+      "ReferenceError (undefined symbol)",
+      4
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 71.0,
+  "elapsed_seconds": 64.1,
   "workers": 1
 }
\ No newline at end of file
diff --git a/lib/js/test262-scoreboard.md b/lib/js/test262-scoreboard.md
index 752301bb..a14c2efd 100644
--- a/lib/js/test262-scoreboard.md
+++ b/lib/js/test262-scoreboard.md
@@ -1,24 +1,22 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 71.0s
+Wall time: 64.1s
 
-**Total:** 46/50 runnable passed (92.0%). Raw: pass=46 fail=2 skip=0 timeout=2 total=50.
+**Total:** 46/50 runnable passed (92.0%). Raw: pass=46 fail=4 skip=0 timeout=0 total=50.
 
 ## Top failure modes
 
-- **2x** Timeout
-- **2x** Test262Error (assertion failed)
+- **4x** ReferenceError (undefined symbol)
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/Number | 46 | 2 | 0 | 2 | 50 | 92.0% |
+| built-ins/Object | 46 | 4 | 0 | 0 | 50 | 92.0% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Number  (46/50 — 92.0%)
+### built-ins/Object  (46/50 — 92.0%)
 
-- **2x** Timeout
-- **2x** Test262Error (assertion failed)
+- **4x** ReferenceError (undefined symbol)
diff --git a/lib/js/transpile.sx b/lib/js/transpile.sx
index c044f558..f717625a 100644
--- a/lib/js/transpile.sx
+++ b/lib/js/transpile.sx
@@ -165,6 +165,8 @@
             (js-transpile-new (nth ast 1) (nth ast 2)))
           ((js-tag? ast "js-class")
             (js-transpile-class (nth ast 1) (nth ast 2) (nth ast 3)))
+          ((js-tag? ast "js-comma")
+            (cons (js-sym "begin") (map js-transpile (nth ast 1))))
           ((js-tag? ast "js-throw") (js-transpile-throw (nth ast 1)))
           ((js-tag? ast "js-try")
             (js-transpile-try (nth ast 1) (nth ast 2) (nth ast 3)))
diff --git a/plans/js-on-sx.md b/plans/js-on-sx.md
index 378f52d5..b98c9a51 100644
--- a/plans/js-on-sx.md
+++ b/plans/js-on-sx.md
@@ -158,6 +158,8 @@ Each item: implement → tests → update progress. Mark `[x]` when tests green.
 
 Append-only record of completed iterations. Loop writes one line per iteration: date, what was done, test count delta.
 
+- 2026-05-08 — **Comma operator `(a, b, c)` parses and evaluates left-to-right, returning last.** Was failing with `Expected punct ')' got punct ','` because `jp-try-arrow-or-paren` only consumed a single assignment expression. Added `jp-parse-comma-seq` / `jp-parse-comma-seq-rest` helpers that build a `js-comma` AST node with the list of expressions; the transpiler emits `(begin ...)` which evaluates each in order and returns the last. Fixes `Object((null,2,3),1,2)`-style tests. built-ins/Object: 44/50 → 46/50. conformance.sh: 148/148.
+
 - 2026-05-08 — **ToPrimitive treats functions as non-primitive in `js-to-string` / `js-to-number`.** Per ES, ToPrimitive only accepts strings/numbers/booleans/null/undefined as primitives — objects AND functions must trigger the next conversion step. Was treating function returns from toString/valueOf as primitives (recursing to extract a string), so a `toString` returning a function wouldn't fall through to `valueOf`. Widened the dict-only check to `(or (= type "dict") (js-function? result))` in both ToPrimitive paths. Now `var o = {toString: () => function(){}, valueOf: () => { throw 'x' }}; new String(o)` propagates `'x'` from valueOf. built-ins/String: 85/99 → 86/99. conformance.sh: 148/148.
 
 - 2026-05-08 — **`fn.toString()` and `String(fn)` honour `Function.prototype.toString` overrides.** Two hardcoded paths returned `"function () { [native code] }"` regardless of any user override: the function-method dispatch in `js-invoke-function-method`, and the lambda branch of `js-to-string`. Both now look up `Function.prototype.toString` via `js-dict-get-walk` and invoke it on the function (`recv`/`v`) when available, falling back to the native marker only if no override exists. Now `Function.prototype.toString = ...; (function(){}).toString()` returns the override, and `new String(fn)` stores the override result. built-ins/String: 84/99 → 85/99. conformance.sh: 148/148.