FIXED: WASM: read a JavaScript object reference back using blob(resolve)

JavaScript objects are now written as <js>(Id,Class) rather than
<js_Class>(Id).  The name between the brackets must be the name of the
blob type for the reader to find the object back, so the blob type is
renamed from `js_object' to `js'.

Writing the class no longer creates an atom (which was never
unregistered): the %As of SfprintfX() quotes it if needed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017dv8qG8JrSfiHguZaFbLAW

Author: JanWielemaker

library/wasm.pl

@@ -247,13 +247,13 @@
 %   Test whether a Prolog term is a JavaScript object.
 
 is_object(Term) :-
-    blob(Term, js_object).
+    blob(Term, js).
 
 is_object(Term, Class), atom(Class) =>
-    blob(Term, js_object),
+    blob(Term, js),
     true := Term.instanceof(Class).
 is_object(Term, Class), var(Class) =>
-    blob(Term, js_object),
+    blob(Term, js),
     Class := Term.instanceof().
 
 

man/wasm.plx

@@ -511,9 +511,10 @@ Instances of \ctype{ArrayBuffer} are translated into a Prolog
 string that consists of characters in the range $0\ldots{}255$.
     \definition{Objects of a one class not being \const{Object}}
 Instances of non-plain JavaScript objects are translated into a
-Prolog \jargon{blob}. Such objects are written as \verb$<js_Class(id)>$.
-The Prolog interface allows for passing the objects back and calling
-methods on them.  See \secref{wasm-js-call}.
+Prolog \jargon{blob}. Such objects are written as
+\verb$<js>(Id,Class)$.  The Prolog interface allows for passing
+the objects back and calling methods on them.  See
+\secref{wasm-js-call}.
 \end{description}
 
 
@@ -614,7 +615,7 @@ following ``functions'' are handled directly by the implementation.
     quotes.  For example:
 \begin{code}
 ?- W := window, T := W.instanceof('Window').
-W = <js_Window>(1),
+W = <js>(1,'Window'),
 T = true.
 \end{code}
     \termitem{-}{Any}
@@ -696,9 +697,9 @@ that await/2 allows, for example, downloading a URL from Prolog:
 \begin{code}
 ?- FP := fetch("test.pl"), await(FP, Response),
    TP := Response.text(), await(TP, T).
-FP = <js_Promise>(4),
-Response = <js_Response>(5),
-TP = <js_Promise>(6),
+FP = <js>(4,'Promise'),
+Response = <js>(5,'Response'),
+TP = <js>(6,'Promise'),
 T = "% :- debug(js) ...".
 \end{code}
 

src/wasm/pl-wasm.c

@@ -159,33 +159,34 @@ typedef struct objref
 } objref;
 
 
-static atom_t
+/* js_obj_class() returns the class name as a malloc'ed UTF-8 string. */
+
+static char *
 js_obj_class(int32_t id)
-{ char *str = (char*)EM_ASM_PTR({
+{ return (char*)EM_ASM_PTR({
       const s = prolog_js_obj_class_name($0);
       const len = lengthBytesUTF8(s)+1;
       const mem = _malloc(len);
       stringToUTF8(s, mem, len);
       return mem;
     }, id);
-  atom_t a = PL_new_atom_mbchars(REP_UTF8, (size_t)-1, str);
-  free(str);
-
-  return a;
 }
 
 
+/* Write a JavaScript object reference as <js>(Id,Class).  The
+ * name between the brackets must be the name of our blob type: that is
+ * what allows read_term/2,3 to find the object back using the option
+ * blob(resolve).  The class is written as a quoted atom.
+ */
+
 static int
 write_jsobj_ref(IOSTREAM *out, atom_t aref, int flags)
 { objref *ref = PL_blob_data(aref, NULL, NULL);
+  char *cname = js_obj_class(ref->id);
   (void)flags;
-  atom_t cname = js_obj_class(ref->id);
-  const wchar_t *s;
 
-  PL_STRINGS_MARK();
-  s = PL_atom_wchars(cname, NULL);
-  SfprintfX(out, "<js_%Ws>(%d)", s, ref->id);
-  PL_STRINGS_RELEASE();
+  SfprintfX(out, "<js>(%d,%UAs)", ref->id, cname);
+  free(cname);
 
   return true;
 }
@@ -206,7 +207,7 @@ save_jsobj_ref(atom_t aref, IOSTREAM *fd)
 { objref *ref = PL_blob_data(aref, NULL, NULL);
   (void)fd;
 
-  return PL_warning("Cannot save reference to <js_object>(%d)",
+  return PL_warning("Cannot save reference to <js>(%d)",
 		    ref->id);
 }
 
@@ -222,7 +223,7 @@ load_jsobj_ref(IOSTREAM *fd)
 static PL_blob_t js_obj_blob =
 { PL_BLOB_MAGIC,
   PL_BLOB_UNIQUE,
-  "js_object",
+  "js",
   release_jsobj_blob,
   NULL,
   write_jsobj_ref,