js-on-sx: Boolean(NaN) === false

js-to-boolean was returning true for NaN because NaN != 0 by IEEE
semantics — the (= v 0) test fell through to the truthy else.
Per ES, NaN is one of the falsy values. Added a
(js-number-is-nan v) clause.
built-ins/Boolean: 19/27 → 21/27. conformance.sh: 148/148.

lib/js/runtime.sx

@@ -1007,6 +1007,7 @@
       ((= v nil) false)
       ((= v false) false)
       ((= v 0) false)
+      ((and (= (type-of v) "number") (js-number-is-nan v)) false)
       ((= v "") false)
       (else true))))
 

lib/js/test262-scoreboard.json

@@ -1,61 +1,45 @@
 {
   "totals": {
-    "pass": 80,
+    "pass": 44,
-    "fail": 11,
+    "fail": 3,
-    "skip": 1,
+    "skip": 0,
-    "timeout": 8,
+    "timeout": 3,
-    "total": 100,
+    "total": 50,
-    "runnable": 99,
+    "runnable": 50,
-    "pass_rate": 80.8
+    "pass_rate": 88.0
   },
   "categories": [
     {
-      "category": "built-ins/String",
+      "category": "built-ins/Number",
-      "total": 100,
+      "total": 50,
-      "pass": 80,
+      "pass": 44,
-      "fail": 11,
+      "fail": 3,
-      "skip": 1,
+      "skip": 0,
-      "timeout": 8,
+      "timeout": 3,
-      "pass_rate": 80.8,
+      "pass_rate": 88.0,
       "top_failures": [
-        [
-          "Test262Error (assertion failed)",
-          9
-        ],
         [
           "Timeout",
-          8
+          3
         ],
         [
-          "ReferenceError (undefined symbol)",
+          "Test262Error (assertion failed)",
-          1
+          3
-        ],
-        [
-          "SyntaxError (parse/unsupported syntax)",
-          1
         ]
       ]
     }
   ],
   "top_failure_modes": [
-    [
-      "Test262Error (assertion failed)",
-      9
-    ],
     [
       "Timeout",
-      8
+      3
     ],
     [
-      "ReferenceError (undefined symbol)",
+      "Test262Error (assertion failed)",
-      1
+      3
-    ],
-    [
-      "SyntaxError (parse/unsupported syntax)",
-      1
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 507.4,
+  "elapsed_seconds": 110.0,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,28 +1,24 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 507.4s
+Wall time: 110.0s
 
-**Total:** 80/99 runnable passed (80.8%). Raw: pass=80 fail=11 skip=1 timeout=8 total=100.
+**Total:** 44/50 runnable passed (88.0%). Raw: pass=44 fail=3 skip=0 timeout=3 total=50.
 
 ## Top failure modes
 
-- **9x** Test262Error (assertion failed)
+- **3x** Timeout
-- **8x** Timeout
+- **3x** Test262Error (assertion failed)
-- **1x** ReferenceError (undefined symbol)
-- **1x** SyntaxError (parse/unsupported syntax)
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/String | 80 | 11 | 1 | 8 | 100 | 80.8% |
+| built-ins/Number | 44 | 3 | 0 | 3 | 50 | 88.0% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/String  (80/99 — 80.8%)
+### built-ins/Number  (44/50 — 88.0%)
 
-- **9x** Test262Error (assertion failed)
+- **3x** Timeout
-- **8x** Timeout
+- **3x** Test262Error (assertion failed)
-- **1x** ReferenceError (undefined symbol)
-- **1x** SyntaxError (parse/unsupported syntax)

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 — **`Boolean(NaN) === false` (and `!NaN === true`).** `js-to-boolean` was returning `true` for NaN because NaN ≠ 0 by IEEE semantics, so the `(= v 0)` test fell through to the truthy-else clause. Per ES, NaN is one of the falsy values. Added a `(js-number-is-nan v)` clause. built-ins/Boolean: 19/27 → 21/27. conformance.sh: 148/148.
+
 - 2026-05-08 — **Global `eval(src)` actually evaluates the source.** Was returning the input string unchanged: `eval('1+2')` returned `"1+2"`, not `3`. Per spec, `eval(string)` parses and evaluates as JS; non-string input passes through. Wired the runtime stub through `js-eval` (which already does the lex/parse/transpile/eval pipeline) when the arg is a string. Fixes `String(eval('var x'))`, the harness internal `eval(...)`, and any test that calls `eval` for runtime evaluation. built-ins/String fail count: 13 → 11. conformance.sh: 148/148.
 
 - 2026-05-08 — **`new <non-callable>` throws TypeError instead of hanging.** `new (new Object(""))` (calling `new` on a String wrapper dict) hung because `js-new-call` called `js-get-ctor-proto` which fell through to `js-ctor-id` which called `inspect ctor` — and `inspect` on a wrapper-with-proto-chain recurses through the prototype's lambdas forever. Added a `(js-function? ctor)` precheck at the top of `js-new-call`: when the receiver isn't callable, raise a `TypeError` instance instead. Now `try { new x } catch(e) { e instanceof TypeError }` returns `true` for non-callable `x`. conformance.sh: 148/148. String 80/99, Array 23/45 maintained.