js-on-sx: Object.assign ToObjects target, throws on null, walks string sources

lib/js/runtime.sx

@@ -4039,20 +4039,45 @@
   (fn
     (&rest args)
     (cond
-      ((= (len args) 0) (dict))
+      ((= (len args) 0)
+        (raise (js-new-call TypeError (js-args "Object.assign called on null or undefined"))))
       (else
         (let
-          ((target (nth args 0)))
-          (for-each
-            (fn
-              (src)
-              (when
-                (dict? src)
+          ((raw-target (nth args 0)))
+          (cond
+            ((or (= raw-target nil) (js-undefined? raw-target))
+              (raise (js-new-call TypeError (js-args "Object.assign called on null or undefined"))))
+            (else
+              (let
+                ((target (js-coerce-this-arg raw-target)))
                 (for-each
-                  (fn (k) (dict-set! target k (get src k)))
-                  (keys src))))
-            (rest args))
-          target)))))
+                  (fn
+                    (src)
+                    (cond
+                      ((or (= src nil) (js-undefined? src)) nil)
+                      ((dict? src)
+                        (for-each
+                          (fn
+                            (k)
+                            (if (js-key-internal? k) nil (dict-set! target k (get src k))))
+                          (js-object-keys src)))
+                      ((= (type-of src) "string")
+                        (let
+                          ((n (len src)))
+                          (begin (js-object-assign-string-loop target src 0 n))))))
+                  (rest args))
+                target))))))))
+
+(define
+  js-object-assign-string-loop
+  (fn
+    (target s i n)
+    (cond
+      ((>= i n) nil)
+      (else
+        (begin
+          (dict-set! target (js-to-string i) (char-at s i))
+          (js-object-assign-string-loop target s (+ i 1) n))))))
 
 (define js-object-freeze (fn (o) o))