js-on-sx: JSON.stringify replacer (fn+array), space, toJSON

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.
 
+- 2026-05-10 — **`JSON.stringify` honours `replacer` (function + array forms), `space`, and `toJSON`.** Previous impl ignored the second/third arguments entirely and never called `toJSON`. Rewrote around a `js-json-serialize-property(key, holder, rep-fn, rep-keys, gap, indent)` core: walks `toJSON` first, then replacer-fn (with `holder` as `this`); arrays-as-replacer become a property-name allowlist; numeric `space` clamped to 0..10 spaces, string `space` truncated to 10 chars, non-empty gap activates indented output with `:` → `: ` separator. Number wrapper / String wrapper / Boolean wrapper unwrap before serialization; non-finite numbers serialize as `"null"`; functions serialize as `undefined`. Result: built-ins/JSON/stringify 6/30 → 14/30 (+8). conformance.sh: 148/148.
+
 - 2026-05-10 — **`JSON.parse` raises spec-correct `SyntaxError` instances and rejects malformed input.** Previously `JSON.parse("12 34")` silently returned `12` (no trailing-content check), `JSON.parse('""')` accepted control chars in strings, an unterminated string read off the end, and the inner `(error "JSON: ...")` calls produced generic Errors not `instanceof SyntaxError`. Added: (1) post-value whitespace skip + trailing-content check in `js-json-parse`; (2) control-char rejection (code < 0x20) and unterminated-string check in `js-json-parse-string-loop`; (3) all internal "JSON: ..." errors now `(raise (js-new-call SyntaxError ...))`. Result: built-ins/JSON/parse 7/30 → 25/30 (+18). JSON 26/30. conformance.sh: 148/148.
 
 - 2026-05-10 — **`arguments` object inside functions is now a mutable list.** `js-arguments-build-form` produced `(cons p1 (cons p2 __extra_args__))` which yielded a structurally-shared (immutable) list — `arguments[1] = 7; arguments[1]++` raised "set-nth!: list is immutable". Wrapping the build in `js-list-copy` so each function entry constructs a fresh mutable list. Existing reads (`arguments.length`, `arguments[i]`) unaffected. Result: language/expressions/postfix-increment 14/30 → 15/30. conformance.sh: 148/148.