fix: preserve NaN through socket parse fallback instead of coercing to null

Swap bare NaN for a sentinel string before JSON.parse and revive it back
to a real NaN so Python-side float(nan) round-trips to the frontend.

Author: FarhanAliRaza

packages/reflex-base/src/reflex_base/.templates/web/utils/state.js

@@ -437,19 +437,22 @@ const resolveSocket = (socket) => {
 
 // Python's json.dumps emits bare Infinity/-Infinity/NaN tokens (invalid JSON).
 // Rewrite them outside string literals so JSON.parse accepts the payload.
-// 1e999 / -1e999 overflow to ±Infinity; NaN has no JSON literal so it becomes null.
+// 1e999 / -1e999 overflow to ±Infinity; NaN has no JSON literal, so it is
+// swapped for a sentinel string and revived back to NaN after parsing.
 // The alternation matches whole string literals first (passed through unchanged),
 // guaranteeing bare-token matches only land in numeric positions.
-const NON_FINITE_FLOAT_RE = /"(?:[^"\\]|\\.)*"|-?Infinity|NaN/g;
+const NAN_SENTINEL = "__reflex_nan__";
+const NON_FINITE_FLOAT_RE = /"(?:[^"\\]|\\.)*"|-?\bInfinity\b|\bNaN\b/g;
 const NON_FINITE_REPLACEMENTS = {
   Infinity: "1e999",
   "-Infinity": "-1e999",
-  NaN: "null",
+  NaN: `"${NAN_SENTINEL}"`,
 };
 const rewriteBareNonFiniteFloats = (str) =>
   str.replace(NON_FINITE_FLOAT_RE, (match) =>
     match[0] === '"' ? match : NON_FINITE_REPLACEMENTS[match],
   );
+const reviveNonFiniteFloats = (_k, v) => (v === NAN_SENTINEL ? NaN : v);
 
 /**
  * Queue events to be processed and trigger processing of queue.
@@ -559,7 +562,10 @@ export const connect = async (
       return JSON.parse(str);
     } catch (e) {
       try {
-        return JSON.parse(rewriteBareNonFiniteFloats(str));
+        return JSON.parse(
+          rewriteBareNonFiniteFloats(str),
+          reviveNonFiniteFloats,
+        );
       } catch (e2) {
         return false;
       }

tests/integration/test_computed_vars.py

@@ -232,7 +232,7 @@ async def test_computed_vars(
 
     special_floats = driver.find_element(By.ID, "special_floats")
     assert special_floats
-    assert special_floats.text == "42.9, , Infinity, -Infinity"
+    assert special_floats.text == "42.9, NaN, Infinity, -Infinity"
 
     increment = driver.find_element(By.ID, "increment")
     assert increment.is_enabled()