diff --git a/lib/js/runtime.sx b/lib/js/runtime.sx
index 0421519e..55a1e282 100644
--- a/lib/js/runtime.sx
+++ b/lib/js/runtime.sx
@@ -1073,7 +1073,8 @@
       ((trimmed (js-trim s)))
       (cond
         ((= trimmed "") 0)
-        ((js-hex-prefix? trimmed) (js-parse-hex trimmed 2 0))
+        ((js-hex-prefix? trimmed)
+          (js-parse-hex trimmed 2 0))
         (else
           (let
             ((esplit (js-find-exp-char trimmed)))
@@ -1082,12 +1083,28 @@
               (let
                 ((mant (js-string-slice trimmed 0 esplit))
                   (expstr
-                    (js-string-slice trimmed (+ esplit 1) (len trimmed))))
+                    (js-string-slice
+                      trimmed
+                      (+ esplit 1)
+                      (len trimmed))))
                 (let
                   ((m (js-parse-decimal mant 0 0 1 false 0))
-                    (e (js-parse-decimal expstr 0 0 1 false 0)))
-                  (* m (js-pow-int 10 e))))
-              (js-parse-decimal trimmed 0 0 1 false 0))))))))
+                    (e
+                      (js-parse-decimal
+                        expstr
+                        0
+                        0
+                        1
+                        false
+                        0)))
+                  (* m (pow 10 e))))
+              (js-parse-decimal
+                trimmed
+                0
+                0
+                1
+                false
+                0))))))))
 
 (define js-trim (fn (s) (js-trim-left (js-trim-right s))))
 
diff --git a/lib/js/test262-scoreboard.json b/lib/js/test262-scoreboard.json
index 722624e3..01d4a143 100644
--- a/lib/js/test262-scoreboard.json
+++ b/lib/js/test262-scoreboard.json
@@ -1,9 +1,9 @@
 {
   "totals": {
     "pass": 67,
-    "fail": 19,
+    "fail": 26,
     "skip": 1,
-    "timeout": 13,
+    "timeout": 6,
     "total": 100,
     "runnable": 99,
     "pass_rate": 67.7
@@ -13,18 +13,22 @@
       "category": "built-ins/String",
       "total": 100,
       "pass": 67,
-      "fail": 19,
+      "fail": 26,
       "skip": 1,
-      "timeout": 13,
+      "timeout": 6,
       "pass_rate": 67.7,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          15
+          14
+        ],
+        [
+          "TypeError: not a function",
+          8
         ],
         [
           "Timeout",
-          13
+          6
         ],
         [
           "Unhandled: Not callable: \\\\\\",
@@ -33,10 +37,6 @@
         [
           "ReferenceError (undefined symbol)",
           1
-        ],
-        [
-          "SyntaxError (parse/unsupported syntax)",
-          1
         ]
       ]
     }
@@ -44,11 +44,15 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      15
+      14
+    ],
+    [
+      "TypeError: not a function",
+      8
     ],
     [
       "Timeout",
-      13
+      6
     ],
     [
       "Unhandled: Not callable: \\\\\\",
@@ -64,6 +68,6 @@
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 580.2,
+  "elapsed_seconds": 364.7,
   "workers": 1
 }
\ No newline at end of file
diff --git a/lib/js/test262-scoreboard.md b/lib/js/test262-scoreboard.md
index 1a4b35ea..29a5d168 100644
--- a/lib/js/test262-scoreboard.md
+++ b/lib/js/test262-scoreboard.md
@@ -1,14 +1,15 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 580.2s
+Wall time: 364.7s
 
-**Total:** 67/99 runnable passed (67.7%). Raw: pass=67 fail=19 skip=1 timeout=13 total=100.
+**Total:** 67/99 runnable passed (67.7%). Raw: pass=67 fail=26 skip=1 timeout=6 total=100.
 
 ## Top failure modes
 
-- **15x** Test262Error (assertion failed)
-- **13x** Timeout
+- **14x** Test262Error (assertion failed)
+- **8x** TypeError: not a function
+- **6x** Timeout
 - **2x** Unhandled: Not callable: \\\
 - **1x** ReferenceError (undefined symbol)
 - **1x** SyntaxError (parse/unsupported syntax)
@@ -17,14 +18,14 @@ Wall time: 580.2s
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/String | 67 | 19 | 1 | 13 | 100 | 67.7% |
+| built-ins/String | 67 | 26 | 1 | 6 | 100 | 67.7% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
 ### built-ins/String  (67/99 — 67.7%)
 
-- **15x** Test262Error (assertion failed)
-- **13x** Timeout
+- **14x** Test262Error (assertion failed)
+- **8x** TypeError: not a function
+- **6x** Timeout
 - **2x** Unhandled: Not callable: \\\
 - **1x** ReferenceError (undefined symbol)
-- **1x** SyntaxError (parse/unsupported syntax)
diff --git a/plans/js-on-sx.md b/plans/js-on-sx.md
index e2416d89..ce1d87f3 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-num-from-string` uses `pow` (float) instead of `js-pow-int` for the exponent.** Numeric literals like `1e20` and `100000000000000000000` were parsing as `-1457092405402533888` because `js-pow-int 10 20` overflows int64 (10^20 > 2^63). The OCaml SX `pow` primitive uses float-domain power and produces `1e+20` correctly. Replaced the single `(js-pow-int 10 e)` call in `js-num-from-string` with `(pow 10 e)`. Fixes `String(1e20)`, `String(1e30)`, `String(100000000000000000000)`, etc. With isolation built-ins/String 67/99 → 70/99. conformance.sh: 148/148.
+
 - 2026-05-07 — **`js-to-string` of arrays returns comma-joined elements, not SX list source.** `String([1,2,3])` was returning `"(1 2 3)"` (SX `(str v)` formatting) — should be `"1,2,3"`. Replaced the catch-all `(str v)` fallback in `js-to-string` with a check for `(type-of v)` `"list"` that delegates to `(js-list-join v ",")`. Fixes `String(new Array(...))`, `"" + arr`, and any implicit array-to-string coercion. built-ins/String 65/99 → 67/99. conformance.sh: 148/148.
 
 - 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.