js-on-sx: object literal spread {...src}

lib/js/parser.sx

@@ -620,6 +620,10 @@
               (append!
                 kvs
                 {:value (jp-parse-assignment st) :computed-key key-expr :key ""}))))
+        ((and (= (get t :type) "punct") (= (get t :value) "..."))
+          (do
+            (jp-advance! st)
+            (append! kvs {:spread (jp-parse-assignment st)})))
         (else (error (str "Unexpected in object: " (get t :type))))))))
 
 (define

lib/js/runtime.sx

@@ -3477,6 +3477,55 @@
         (dict-set! obj sk val)
         val))))
 
+(define
+  js-obj-spread!
+  (fn
+    (target src)
+    (cond
+      ((or (= src nil) (js-undefined? src)) target)
+      ((dict? src)
+        (begin
+          (for-each
+            (fn
+              (k)
+              (if
+                (js-key-internal? k)
+                nil
+                (js-obj-set! target k (get src k))))
+            (js-object-keys src))
+          target))
+      ((= (type-of src) "string")
+        (let
+          ((n (len src)))
+          (begin (js-obj-spread-string-loop! target src 0 n) target)))
+      ((list? src)
+        (let
+          ((n (len src)))
+          (begin (js-obj-spread-list-loop! target src 0 n) target)))
+      (else target))))
+
+(define
+  js-obj-spread-string-loop!
+  (fn
+    (target s i n)
+    (cond
+      ((>= i n) nil)
+      (else
+        (begin
+          (js-obj-set! target (js-to-string i) (char-at s i))
+          (js-obj-spread-string-loop! target s (+ i 1) n))))))
+
+(define
+  js-obj-spread-list-loop!
+  (fn
+    (target arr i n)
+    (cond
+      ((>= i n) nil)
+      (else
+        (begin
+          (js-obj-set! target (js-to-string i) (nth arr i))
+          (js-obj-spread-list-loop! target arr (+ i 1) n))))))
+
 (begin
   (define
     js-set-prop

lib/js/transpile.sx

@@ -482,14 +482,21 @@
           (map
             (fn
               (entry)
-              (list
-                (js-sym "js-obj-set!")
-                (js-sym "_obj")
-                (if
-                  (contains? (keys entry) :computed-key)
-                  (list (js-sym "js-to-string") (js-transpile (get entry :computed-key)))
-                  (get entry :key))
-                (js-transpile (get entry :value))))
+              (cond
+                ((contains? (keys entry) :spread)
+                  (list
+                    (js-sym "js-obj-spread!")
+                    (js-sym "_obj")
+                    (js-transpile (get entry :spread))))
+                (else
+                  (list
+                    (js-sym "js-obj-set!")
+                    (js-sym "_obj")
+                    (if
+                      (contains? (keys entry) :computed-key)
+                      (list (js-sym "js-to-string") (js-transpile (get entry :computed-key)))
+                      (get entry :key))
+                    (js-transpile (get entry :value))))))
             entries)
           (list (js-sym "_obj")))))))