diff --git a/lib/js/lexer.sx b/lib/js/lexer.sx
index abf28b75..13f82904 100644
--- a/lib/js/lexer.sx
+++ b/lib/js/lexer.sx
@@ -29,6 +29,16 @@
       (and (>= c "a") (<= c "f"))
       (and (>= c "A") (<= c "F")))))
 
+(define
+  js-hex-value
+  (fn
+    (c)
+    (cond
+      ((and (>= c "0") (<= c "9")) (- (char-code c) 48))
+      ((and (>= c "a") (<= c "f")) (- (char-code c) 87))
+      ((and (>= c "A") (<= c "F")) (- (char-code c) 55))
+      (else 0))))
+
 (define
   js-letter?
   (fn (c) (or (and (>= c "a") (<= c "z")) (and (>= c "A") (<= c "Z")))))
@@ -37,9 +47,9 @@
 
 (define js-ident-char? (fn (c) (or (js-ident-start? c) (js-digit? c))))
 
+;; ── Reserved words ────────────────────────────────────────────────
 (define js-ws? (fn (c) (or (= c " ") (= c "\t") (= c "\n") (= c "\r"))))
 
-;; ── Reserved words ────────────────────────────────────────────────
 (define
   js-keywords
   (list
@@ -86,15 +96,18 @@
     "await"
     "of"))
 
+;; ── Main tokenizer ────────────────────────────────────────────────
 (define js-keyword? (fn (word) (contains? js-keywords word)))
 
-;; ── Main tokenizer ────────────────────────────────────────────────
 (define
   js-tokenize
   (fn
     (src)
     (let
-      ((tokens (list)) (pos 0) (src-len (len src)) (nl-before false))
+      ((tokens (list))
+        (pos 0)
+        (src-len (len src))
+        (nl-before false))
       (define
         js-peek
         (fn
@@ -109,7 +122,7 @@
           (let
             ((sl (len s)))
             (and (<= (+ pos sl) src-len) (= (slice src pos (+ pos sl)) s)))))
-      (define js-emit! (fn (type value start) (append! tokens {:pos start :value value :type type :nl nl-before})))
+      (define js-emit! (fn (type value start) (append! tokens {:nl nl-before :type type :value value :pos start})))
       (define
         skip-line-comment!
         (fn
@@ -256,11 +269,55 @@
                               ((= ch "b") (append! chars "\\b"))
                               ((= ch "f") (append! chars "\\f"))
                               ((= ch "v") (append! chars "\\v"))
+                              ((= ch "u")
+                                (if
+                                  (and
+                                    (< (+ pos 4) src-len)
+                                    (js-hex-digit? (js-peek 1))
+                                    (js-hex-digit? (js-peek 2))
+                                    (js-hex-digit? (js-peek 3))
+                                    (js-hex-digit? (js-peek 4)))
+                                  (do
+                                    (append!
+                                      chars
+                                      (char-from-code
+                                        (+
+                                          (*
+                                            4096
+                                            (js-hex-value
+                                              (js-peek 1)))
+                                          (*
+                                            256
+                                            (js-hex-value
+                                              (js-peek 2)))
+                                          (*
+                                            16
+                                            (js-hex-value
+                                              (js-peek 3)))
+                                          (js-hex-value (js-peek 4)))))
+                                    (advance! 4))
+                                  (append! chars ch)))
+                              ((= ch "x")
+                                (if
+                                  (and
+                                    (< (+ pos 2) src-len)
+                                    (js-hex-digit? (js-peek 1))
+                                    (js-hex-digit? (js-peek 2)))
+                                  (do
+                                    (append!
+                                      chars
+                                      (char-from-code
+                                        (+
+                                          (* 16 (js-hex-value (js-peek 1)))
+                                          (js-hex-value (js-peek 2)))))
+                                    (advance! 2))
+                                  (append! chars ch)))
                               (else (append! chars ch)))
                             (advance! 1))))
                       (loop)))
                   ((= (cur) quote-char) (advance! 1))
-                  (else (do (append! chars (cur)) (advance! 1) (loop))))))
+                  (else
+                    (do (append! chars (cur)) (advance! 1) (loop))))))
             (loop)
             (join "" chars))))
       (define
@@ -291,7 +348,8 @@
                       ()
                       (cond
                         ((>= pos src-len) nil)
-                        ((and (= (cur) "}") (= depth 1)) (advance! 1))
+                        ((and (= (cur) "}") (= depth 1))
+                          (advance! 1))
                         ((= (cur) "}")
                           (do
                             (append! buf (cur))
@@ -327,7 +385,9 @@
                                             (advance! 1)))
                                         (sloop)))
                                     ((= (cur) q)
-                                      (do (append! buf (cur)) (advance! 1)))
+                                      (do
+                                        (append! buf (cur))
+                                        (advance! 1)))
                                     (else
                                       (do
                                         (append! buf (cur))
@@ -336,7 +396,10 @@
                               (sloop)
                               (expr-loop))))
                         (else
-                          (do (append! buf (cur)) (advance! 1) (expr-loop))))))
+                          (do
+                            (append! buf (cur))
+                            (advance! 1)
+                            (expr-loop))))))
                   (expr-loop)
                   (join "" buf))))
             (define
@@ -378,14 +441,17 @@
                               (else (append! chars ch)))
                             (advance! 1))))
                       (loop)))
-                  (else (do (append! chars (cur)) (advance! 1) (loop))))))
+                  (else
+                    (do (append! chars (cur)) (advance! 1) (loop))))))
             (loop)
             (flush-chars!)
             (if
               (= (len parts) 0)
               ""
               (if
-                (and (= (len parts) 1) (= (nth (nth parts 0) 0) "str"))
+                (and
+                  (= (len parts) 1)
+                  (= (nth (nth parts 0) 0) "str"))
                 (nth (nth parts 0) 1)
                 parts)))))
       (define
@@ -455,9 +521,13 @@
                       (append! buf (cur))
                       (advance! 1)
                       (body-loop)))
-                  ((and (= (cur) "/") (not in-class)) (advance! 1))
+                  ((and (= (cur) "/") (not in-class))
+                    (advance! 1))
                   (else
-                    (begin (append! buf (cur)) (advance! 1) (body-loop))))))
+                    (begin
+                      (append! buf (cur))
+                      (advance! 1)
+                      (body-loop))))))
             (body-loop)
             (let
               ((flags-buf (list)))
@@ -472,7 +542,7 @@
                       (advance! 1)
                       (flags-loop)))))
               (flags-loop)
-              {:pattern (join "" buf) :flags (join "" flags-buf)}))))
+              {:flags (join "" flags-buf) :pattern (join "" buf)}))))
       (define
         try-op-4!
         (fn
@@ -512,58 +582,104 @@
         (fn
           (start)
           (cond
-            ((at? "==") (do (js-emit! "op" "==" start) (advance! 2) true))
-            ((at? "!=") (do (js-emit! "op" "!=" start) (advance! 2) true))
-            ((at? "<=") (do (js-emit! "op" "<=" start) (advance! 2) true))
-            ((at? ">=") (do (js-emit! "op" ">=" start) (advance! 2) true))
-            ((at? "&&") (do (js-emit! "op" "&&" start) (advance! 2) true))
-            ((at? "||") (do (js-emit! "op" "||" start) (advance! 2) true))
-            ((at? "??") (do (js-emit! "op" "??" start) (advance! 2) true))
-            ((at? "=>") (do (js-emit! "op" "=>" start) (advance! 2) true))
-            ((at? "**") (do (js-emit! "op" "**" start) (advance! 2) true))
-            ((at? "<<") (do (js-emit! "op" "<<" start) (advance! 2) true))
-            ((at? ">>") (do (js-emit! "op" ">>" start) (advance! 2) true))
-            ((at? "++") (do (js-emit! "op" "++" start) (advance! 2) true))
-            ((at? "--") (do (js-emit! "op" "--" start) (advance! 2) true))
-            ((at? "+=") (do (js-emit! "op" "+=" start) (advance! 2) true))
-            ((at? "-=") (do (js-emit! "op" "-=" start) (advance! 2) true))
-            ((at? "*=") (do (js-emit! "op" "*=" start) (advance! 2) true))
-            ((at? "/=") (do (js-emit! "op" "/=" start) (advance! 2) true))
-            ((at? "%=") (do (js-emit! "op" "%=" start) (advance! 2) true))
-            ((at? "&=") (do (js-emit! "op" "&=" start) (advance! 2) true))
-            ((at? "|=") (do (js-emit! "op" "|=" start) (advance! 2) true))
-            ((at? "^=") (do (js-emit! "op" "^=" start) (advance! 2) true))
-            ((at? "?.") (do (js-emit! "op" "?." start) (advance! 2) true))
+            ((at? "==")
+              (do (js-emit! "op" "==" start) (advance! 2) true))
+            ((at? "!=")
+              (do (js-emit! "op" "!=" start) (advance! 2) true))
+            ((at? "<=")
+              (do (js-emit! "op" "<=" start) (advance! 2) true))
+            ((at? ">=")
+              (do (js-emit! "op" ">=" start) (advance! 2) true))
+            ((at? "&&")
+              (do (js-emit! "op" "&&" start) (advance! 2) true))
+            ((at? "||")
+              (do (js-emit! "op" "||" start) (advance! 2) true))
+            ((at? "??")
+              (do (js-emit! "op" "??" start) (advance! 2) true))
+            ((at? "=>")
+              (do (js-emit! "op" "=>" start) (advance! 2) true))
+            ((at? "**")
+              (do (js-emit! "op" "**" start) (advance! 2) true))
+            ((at? "<<")
+              (do (js-emit! "op" "<<" start) (advance! 2) true))
+            ((at? ">>")
+              (do (js-emit! "op" ">>" start) (advance! 2) true))
+            ((at? "++")
+              (do (js-emit! "op" "++" start) (advance! 2) true))
+            ((at? "--")
+              (do (js-emit! "op" "--" start) (advance! 2) true))
+            ((at? "+=")
+              (do (js-emit! "op" "+=" start) (advance! 2) true))
+            ((at? "-=")
+              (do (js-emit! "op" "-=" start) (advance! 2) true))
+            ((at? "*=")
+              (do (js-emit! "op" "*=" start) (advance! 2) true))
+            ((at? "/=")
+              (do (js-emit! "op" "/=" start) (advance! 2) true))
+            ((at? "%=")
+              (do (js-emit! "op" "%=" start) (advance! 2) true))
+            ((at? "&=")
+              (do (js-emit! "op" "&=" start) (advance! 2) true))
+            ((at? "|=")
+              (do (js-emit! "op" "|=" start) (advance! 2) true))
+            ((at? "^=")
+              (do (js-emit! "op" "^=" start) (advance! 2) true))
+            ((at? "?.")
+              (do (js-emit! "op" "?." start) (advance! 2) true))
             (else false))))
       (define
         emit-one-op!
         (fn
           (ch start)
           (cond
-            ((= ch "(") (do (js-emit! "punct" "(" start) (advance! 1)))
-            ((= ch ")") (do (js-emit! "punct" ")" start) (advance! 1)))
-            ((= ch "[") (do (js-emit! "punct" "[" start) (advance! 1)))
-            ((= ch "]") (do (js-emit! "punct" "]" start) (advance! 1)))
-            ((= ch "{") (do (js-emit! "punct" "{" start) (advance! 1)))
-            ((= ch "}") (do (js-emit! "punct" "}" start) (advance! 1)))
-            ((= ch ",") (do (js-emit! "punct" "," start) (advance! 1)))
-            ((= ch ";") (do (js-emit! "punct" ";" start) (advance! 1)))
-            ((= ch ":") (do (js-emit! "punct" ":" start) (advance! 1)))
-            ((= ch ".") (do (js-emit! "punct" "." start) (advance! 1)))
-            ((= ch "?") (do (js-emit! "op" "?" start) (advance! 1)))
-            ((= ch "+") (do (js-emit! "op" "+" start) (advance! 1)))
-            ((= ch "-") (do (js-emit! "op" "-" start) (advance! 1)))
-            ((= ch "*") (do (js-emit! "op" "*" start) (advance! 1)))
-            ((= ch "/") (do (js-emit! "op" "/" start) (advance! 1)))
-            ((= ch "%") (do (js-emit! "op" "%" start) (advance! 1)))
-            ((= ch "=") (do (js-emit! "op" "=" start) (advance! 1)))
-            ((= ch "<") (do (js-emit! "op" "<" start) (advance! 1)))
-            ((= ch ">") (do (js-emit! "op" ">" start) (advance! 1)))
-            ((= ch "!") (do (js-emit! "op" "!" start) (advance! 1)))
-            ((= ch "&") (do (js-emit! "op" "&" start) (advance! 1)))
-            ((= ch "|") (do (js-emit! "op" "|" start) (advance! 1)))
-            ((= ch "^") (do (js-emit! "op" "^" start) (advance! 1)))
-            ((= ch "~") (do (js-emit! "op" "~" start) (advance! 1)))
+            ((= ch "(")
+              (do (js-emit! "punct" "(" start) (advance! 1)))
+            ((= ch ")")
+              (do (js-emit! "punct" ")" start) (advance! 1)))
+            ((= ch "[")
+              (do (js-emit! "punct" "[" start) (advance! 1)))
+            ((= ch "]")
+              (do (js-emit! "punct" "]" start) (advance! 1)))
+            ((= ch "{")
+              (do (js-emit! "punct" "{" start) (advance! 1)))
+            ((= ch "}")
+              (do (js-emit! "punct" "}" start) (advance! 1)))
+            ((= ch ",")
+              (do (js-emit! "punct" "," start) (advance! 1)))
+            ((= ch ";")
+              (do (js-emit! "punct" ";" start) (advance! 1)))
+            ((= ch ":")
+              (do (js-emit! "punct" ":" start) (advance! 1)))
+            ((= ch ".")
+              (do (js-emit! "punct" "." start) (advance! 1)))
+            ((= ch "?")
+              (do (js-emit! "op" "?" start) (advance! 1)))
+            ((= ch "+")
+              (do (js-emit! "op" "+" start) (advance! 1)))
+            ((= ch "-")
+              (do (js-emit! "op" "-" start) (advance! 1)))
+            ((= ch "*")
+              (do (js-emit! "op" "*" start) (advance! 1)))
+            ((= ch "/")
+              (do (js-emit! "op" "/" start) (advance! 1)))
+            ((= ch "%")
+              (do (js-emit! "op" "%" start) (advance! 1)))
+            ((= ch "=")
+              (do (js-emit! "op" "=" start) (advance! 1)))
+            ((= ch "<")
+              (do (js-emit! "op" "<" start) (advance! 1)))
+            ((= ch ">")
+              (do (js-emit! "op" ">" start) (advance! 1)))
+            ((= ch "!")
+              (do (js-emit! "op" "!" start) (advance! 1)))
+            ((= ch "&")
+              (do (js-emit! "op" "&" start) (advance! 1)))
+            ((= ch "|")
+              (do (js-emit! "op" "|" start) (advance! 1)))
+            ((= ch "^")
+              (do (js-emit! "op" "^" start) (advance! 1)))
+            ((= ch "~")
+              (do (js-emit! "op" "~" start) (advance! 1)))
             (else (advance! 1)))))
       (define
         scan!
diff --git a/lib/js/test262-scoreboard.json b/lib/js/test262-scoreboard.json
index 58e45ede..852e7b94 100644
--- a/lib/js/test262-scoreboard.json
+++ b/lib/js/test262-scoreboard.json
@@ -1,9 +1,9 @@
 {
   "totals": {
     "pass": 65,
-    "fail": 26,
+    "fail": 28,
     "skip": 1,
-    "timeout": 8,
+    "timeout": 6,
     "total": 100,
     "runnable": 99,
     "pass_rate": 65.7
@@ -13,9 +13,9 @@
       "category": "built-ins/String",
       "total": 100,
       "pass": 65,
-      "fail": 26,
+      "fail": 28,
       "skip": 1,
-      "timeout": 8,
+      "timeout": 6,
       "pass_rate": 65.7,
       "top_failures": [
         [
@@ -23,11 +23,11 @@
           16
         ],
         [
-          "Timeout",
+          "TypeError: not a function",
           8
         ],
         [
-          "TypeError: not a function",
+          "Timeout",
           6
         ],
         [
@@ -47,11 +47,11 @@
       16
     ],
     [
-      "Timeout",
+      "TypeError: not a function",
       8
     ],
     [
-      "TypeError: not a function",
+      "Timeout",
       6
     ],
     [
@@ -68,6 +68,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 420.4,
+  "elapsed_seconds": 353.1,
   "workers": 1
 }
\ No newline at end of file
diff --git a/lib/js/test262-scoreboard.md b/lib/js/test262-scoreboard.md
index 9eca91c0..40d688ce 100644
--- a/lib/js/test262-scoreboard.md
+++ b/lib/js/test262-scoreboard.md
@@ -1,15 +1,15 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 420.4s
+Wall time: 353.1s
 
-**Total:** 65/99 runnable passed (65.7%). Raw: pass=65 fail=26 skip=1 timeout=8 total=100.
+**Total:** 65/99 runnable passed (65.7%). Raw: pass=65 fail=28 skip=1 timeout=6 total=100.
 
 ## Top failure modes
 
 - **16x** Test262Error (assertion failed)
-- **8x** Timeout
-- **6x** TypeError: not a function
+- **8x** TypeError: not a function
+- **6x** Timeout
 - **2x** Unhandled: Not callable: \\\
 - **1x** ReferenceError (undefined symbol)
 - **1x** SyntaxError (parse/unsupported syntax)
@@ -18,14 +18,14 @@ Wall time: 420.4s
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/String | 65 | 26 | 1 | 8 | 100 | 65.7% |
+| built-ins/String | 65 | 28 | 1 | 6 | 100 | 65.7% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
 ### built-ins/String  (65/99 — 65.7%)
 
 - **16x** Test262Error (assertion failed)
-- **8x** Timeout
-- **6x** TypeError: not a function
+- **8x** TypeError: not a function
+- **6x** Timeout
 - **2x** Unhandled: Not callable: \\\
 - **1x** ReferenceError (undefined symbol)
diff --git a/plans/js-on-sx.md b/plans/js-on-sx.md
index 663e0bd8..5fc77465 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.
 
+- 2026-05-07 — **JS lexer: handle `\uXXXX` and `\xXX` escape sequences in string literals.** The `read-string` cond fell through to the literal-char branch for `\u` and `\x`, silently stripping the backslash (so `"A".length` returned 5 instead of 1). Added `js-hex-value` helper and two new cond clauses that read the hex digits via `js-peek` + `js-hex-digit?`, compute the code point, and emit it via `char-from-code`. Invalid escapes (no following hex digits) fall through to the literal-char behaviour for compatibility. With test isolation (`--restart-every 1`) built-ins/String 65/99 → 68/99. Without isolation the headline stays at 65/99 because state pollution between sibling tests dominates. conformance.sh: 148/148.
+
 - 2026-05-07 — **Bump test262 runner default per-test timeout 5s→15s.** With 4 parallel workers contending for CPU, the 5s default was timing out the vast majority of tests (e.g. 85/99 on built-ins/String). Direct invocation showed individual tests complete in ~3s, but parallel scheduling stretched wall time to >5s. Bumping to 15s makes the scoreboard usable: built-ins/String 14.1% → 65.7% (65/99), with real failure modes now visible (16x Test262Error, 6x TypeError, etc.) instead of "85x Timeout" drowning the signal. Regenerated scoreboard to reflect the new state. conformance.sh: 148/148.
 
 - 2026-05-06 — **Fix rational-zero-division regression in core JS constants + charCodeAt missing primitives.** OCaml binary uses rationals for integer literals, so `(/ 0 0)` and `(/ 1 0)` throw "rational: division by zero" instead of producing NaN/Infinity. Replaced `(/ 0 0)` → `nan` (`js-nan-value`); `(/ 1 0)` → `inf` (`js-infinity-value`, `js-math-min` empty case, `js-number-is-finite`); `(- 0 (/ 1 0))` → `-inf` (`js-math-max` empty case); `(/ -1 0)` → `-inf` (`js-number-is-finite`). `js-max-value-approx` was looping forever (rationals never reach float infinity) — replaced with literal `1.7976931348623157e+308`. Fixed `charCodeAt` and string `.length` to use `(len s)` and `(char-code (char-at s idx))` instead of missing `unicode-len`/`unicode-char-code-at` primitives. conformance.sh: 0→148/148. Unit tests: 521/530 best run (baseline run was 417/530; both timeout-flaky).