js-on-sx: spread ... in array literals and call args

Parser: jp-array-loop and jp-call-args-loop detect punct "..."
and emit (js-spread inner).

Transpile: when any element is spread, build array/args via
js-array-spread-build with (list "js-value" v) and (list
"js-spread" xs) tags.

Runtime: js-array-spread-build walks items, appending values or
splicing spreads via js-iterable-to-list (handles list/string/dict).

Works in arrays, call args, variadic fns (Math.max(...arr)),
and string spread ([...'abc']).

414/416 unit (+5), 148/148 slice unchanged.

lib/js/parser.sx

@@ -486,11 +486,18 @@
     (cond
       ((jp-at? st "punct" "]") nil)
       (else
-        (do
+        (begin
-          (append! elems (jp-parse-assignment st))
+          (cond
+            ((jp-at? st "punct" "...")
+              (begin
+                (jp-advance! st)
+                (append!
+                  elems
+                  (list (quote js-spread) (jp-parse-assignment st)))))
+            (else (append! elems (jp-parse-assignment st))))
           (cond
             ((jp-at? st "punct" ",")
-              (do (jp-advance! st) (jp-array-loop st elems)))
+              (begin (jp-advance! st) (jp-array-loop st elems)))
             (else nil)))))))
 
 ;; ── Entry point ─────────────────────────────────────────────────
@@ -600,11 +607,18 @@
     (cond
       ((jp-at? st "punct" ")") nil)
       (else
-        (do
+        (begin
-          (append! args (jp-parse-assignment st))
+          (cond
+            ((jp-at? st "punct" "...")
+              (begin
+                (jp-advance! st)
+                (append!
+                  args
+                  (list (quote js-spread) (jp-parse-assignment st)))))
+            (else (append! args (jp-parse-assignment st))))
           (cond
             ((jp-at? st "punct" ",")
-              (do (jp-advance! st) (jp-call-args-loop st args)))
+              (begin (jp-advance! st) (jp-call-args-loop st args)))
             (else nil)))))))
 
 (define

lib/js/runtime.sx

@@ -1750,6 +1750,26 @@
 
 (define Object {:entries js-object-entries :values js-object-values :freeze js-object-freeze :assign js-object-assign :keys js-object-keys})
 
+(define
+  js-array-spread-build
+  (fn
+    (&rest items)
+    (let
+      ((result (list)))
+      (for-each
+        (fn
+          (item)
+          (let
+            ((kind (nth item 0)))
+            (cond
+              ((= kind "js-spread")
+                (for-each
+                  (fn (x) (append! result x))
+                  (js-iterable-to-list (nth item 1))))
+              (else (append! result (nth item 1))))))
+        items)
+      result)))
+
 (define js-array-is-array (fn (v) (list? v)))
 
 (define js-array-of (fn (&rest args) args))

lib/js/test.sh

@@ -1059,6 +1059,18 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 2401)
 (eval "(js-eval \"'abcd'.slice('1', '3')\")")
 
+;; ── Phase 11.spread: ... in arrays and calls ───────────────────
+(epoch 2500)
+(eval "(js-eval \"var a=[1,2]; var b=[...a,3,4]; b.length\")")
+(epoch 2501)
+(eval "(js-eval \"var a=[1,2]; var b=[0,...a,3]; b.join(',')\")")
+(epoch 2502)
+(eval "(js-eval \"function f(a,b,c){ return a+b+c; } var args=[1,2,3]; f(...args)\")")
+(epoch 2503)
+(eval "(js-eval \"Math.max(...[1,5,3])\")")
+(epoch 2504)
+(eval "(js-eval \"var a=[...'abc']; a.length\")")
+
 EPOCHS
 
 
@@ -1629,6 +1641,13 @@ check 2307 "Array.from w/ map"             '"2,4,6"'
 check 2400 "charAt coerces string"         '"c"'
 check 2401 "slice coerces strings"         '"bc"'
 
+# ── Phase 11.spread ───────────────────────────────────────────
+check 2500 "spread in array length"        '4'
+check 2501 "spread middle of array"        '"0,1,2,3"'
+check 2502 "spread in call args"           '6'
+check 2503 "spread Math.max"               '5'
+check 2504 "spread string"                 '3'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "✓ $PASS/$TOTAL JS-on-SX tests passed"

lib/js/transpile.sx

@@ -254,15 +254,15 @@
   (fn
     (callee args)
     (cond
-      ((and (list? callee) (js-tag? callee "js-member"))
+      ((and (js-tag? callee "js-member") (not (js-has-spread? args)))
         (let
           ((recv (js-transpile (nth callee 1))) (key (nth callee 2)))
           (list
             (js-sym "js-invoke-method")
             recv
             key
-            (cons (js-sym "list") (map js-transpile args)))))
+            (js-transpile-args args))))
-      ((and (list? callee) (js-tag? callee "js-index"))
+      ((and (js-tag? callee "js-index") (not (js-has-spread? args)))
         (let
           ((recv (js-transpile (nth callee 1)))
             (key (js-transpile (nth callee 2))))
@@ -270,12 +270,29 @@
             (js-sym "js-invoke-method-dyn")
             recv
             key
-            (cons (js-sym "list") (map js-transpile args)))))
+            (js-transpile-args args))))
+      ((js-tag? callee "js-member")
+        (let
+          ((recv (js-transpile (nth callee 1))) (key (nth callee 2)))
+          (list
+            (js-sym "js-invoke-method")
+            recv
+            key
+            (js-transpile-args args))))
+      ((js-tag? callee "js-index")
+        (let
+          ((recv (js-transpile (nth callee 1)))
+            (key (js-transpile (nth callee 2))))
+          (list
+            (js-sym "js-invoke-method-dyn")
+            recv
+            key
+            (js-transpile-args args))))
       (else
         (list
           (js-sym "js-call-plain")
           (js-transpile callee)
-          (cons (js-sym "list") (map js-transpile args)))))))
+          (js-transpile-args args))))))
 
 ;; ── Array literal ─────────────────────────────────────────────────
 
@@ -295,10 +312,58 @@
 ;; order and allows computed values.
 (define
   js-transpile-array
-  (fn (elts) (cons (js-sym "list") (map js-transpile elts))))
+  (fn
+    (elts)
+    (if
+      (js-has-spread? elts)
+      (cons
+        (js-sym "js-array-spread-build")
+        (map
+          (fn
+            (e)
+            (if
+              (js-tag? e "js-spread")
+              (list (js-sym "list") "js-spread" (js-transpile (nth e 1)))
+              (list (js-sym "list") "js-value" (js-transpile e))))
+          elts))
+      (cons (js-sym "list") (map js-transpile elts)))))
 
 ;; ── Conditional ───────────────────────────────────────────────────
 
+(define
+  js-has-spread?
+  (fn
+    (lst)
+    (cond
+      ((empty? lst) false)
+      ((js-tag? (first lst) "js-spread") true)
+      (else (js-has-spread? (rest lst))))))
+
+;; ── Arrow function ────────────────────────────────────────────────
+
+(define
+  js-transpile-args
+  (fn
+    (args)
+    (if
+      (js-has-spread? args)
+      (cons
+        (js-sym "js-array-spread-build")
+        (map
+          (fn
+            (e)
+            (if
+              (js-tag? e "js-spread")
+              (list (js-sym "list") "js-spread" (js-transpile (nth e 1)))
+              (list (js-sym "list") "js-value" (js-transpile e))))
+          args))
+      (cons (js-sym "list") (map js-transpile args)))))
+
+;; ── Assignment ────────────────────────────────────────────────────
+
+;; `a = b` on an ident → (set! a b).
+;; `a += b` on an ident → (set! a (js-add a b)).
+;; `obj.k = v` / `obj[k] = v` → (js-set-prop obj "k" v).
 (define
   js-transpile-object
   (fn
@@ -320,8 +385,6 @@
             entries)
           (list (js-sym "_obj")))))))
 
-;; ── Arrow function ────────────────────────────────────────────────
-
 (define
   js-transpile-cond
   (fn
@@ -332,11 +395,6 @@
       (js-transpile t)
       (js-transpile f))))
 
-;; ── Assignment ────────────────────────────────────────────────────
-
-;; `a = b` on an ident → (set! a b).
-;; `a += b` on an ident → (set! a (js-add a b)).
-;; `obj.k = v` / `obj[k] = v` → (js-set-prop obj "k" v).
 (define
   js-transpile-arrow
   (fn
@@ -367,6 +425,9 @@
                 (append inits (list (js-transpile body))))))))
       (list (js-sym "fn") param-syms body-tr))))
 
+;; ── End-to-end entry points ───────────────────────────────────────
+
+;; Transpile + eval a single JS expression string.
 (define
   js-transpile-tpl
   (fn
@@ -378,6 +439,8 @@
       (else
         (cons (js-sym "js-template-concat") (js-transpile-tpl-parts parts))))))
 
+;; Transpile a JS expression string to SX source text (for inspection
+;; in tests). Useful for asserting the exact emitted tree.
 (define
   js-transpile-tpl-parts
   (fn
@@ -389,9 +452,6 @@
         (js-transpile (first parts))
         (js-transpile-tpl-parts (rest parts))))))
 
-;; ── End-to-end entry points ───────────────────────────────────────
-
-;; Transpile + eval a single JS expression string.
 (define
   js-transpile-assign
   (fn
@@ -429,8 +489,6 @@
             (js-transpile rhs))))
       (else (error "js-transpile-assign: unsupported target")))))
 
-;; Transpile a JS expression string to SX source text (for inspection
-;; in tests). Useful for asserting the exact emitted tree.
 (define
   js-compound-update
   (fn

plans/js-on-sx.md

@@ -191,6 +191,8 @@ Append-only record of completed iterations. Loop writes one line per iteration:
 
 - 2026-04-23 — **Array.prototype flat/fill; indexOf start arg; for..of/for..in.** Array: `flat(depth=1)` uses `js-list-flat-loop` (recursive flatten), `fill(value, start?, end?)` mutates in-place then returns self via `js-list-fill-loop`. Fixed `indexOf` to honor the `fromIndex` second argument. Parser: `jp-parse-for-stmt` now does a 2-token lookahead — if it sees `(var? ident (of|in) expr)` it emits `(js-for-of-in kind ident iter body)`, else falls back to classic `for(;;)`. Transpile: `js-transpile-for-of-in` wraps body in `(call/cc (fn (__break__) (let ((__js_items__ <normalized-source>)) (for-each (fn (ident) (call/cc (fn (__continue__) body))) items))))`. For `of` it normalizes via `js-iterable-to-list` (list → self, string → char list, dict → values). For `in` it iterates over `js-object-keys`. `break` / `continue` already route to the call/cc bindings. 8 new tests (flat, fill variants, indexOf with start, for-of array/string, for-in dict), **399/401** (391→+8). Conformance unchanged. Gotcha: **SX `cond` clauses evaluate only the last expr of a body. `(cond ((test) (set! a 1) (set! b 2)) …)` silently drops the first set!.** Must wrap multi-stmt clause bodies in `(begin …)`. First pass on the for-stmt rewrite had multi-expr cond clauses that silently did nothing — broke all existing for-loop tests, not just the new ones.
 
+- 2026-04-23 — **String.replace/search/match + Array.from; js-num-to-int coerces strings; spread operator `...`.** Strings: `replace(regex|str, repl)`, `search(regex|str)`, `match(regex|str)` all handle both regex and plain-string args. Regex path walks via `js-string-index-of` with case-adjusted hay/needle. Array.from(iterable, mapFn?) via `js-iterable-to-list`. `js-num-to-int` now routes through `js-to-number` so `'abcd'.charAt('2')` and `.slice('1','3')` coerce properly. **Spread `...` in array literals and call args.** Parser: `jp-array-loop` and `jp-call-args-loop` detect `punct "..."` and emit `(js-spread inner)` entries. Transpile: if any element has a spread, the array/args list is built via `(js-array-spread-build (list "js-value" v) (list "js-spread" xs) ...)`. Runtime `js-array-spread-build` walks items, appending values directly and splicing spread via `js-iterable-to-list`. Works in call args (including variadic `Math.max(...arr)`) and in array literals (prefix, middle, and string-spread `[...'abc']`). Gotcha: early pass used `(js-sym ":js-spread")` thinking it'd make a keyword — `js-sym` makes a SYMBOL which becomes an env lookup (and fails as undefined). Use plain STRING `"js-spread"` as the discriminator. 10 new tests (replace/search/match both arg types, Array.from, coercion, 5 spread variants), **414/416** (399→+15). Conformance unchanged.
+
 ## Phase 3-5 gotchas
 
 Worth remembering for later phases: