Add C API function JS_GetClassID()

If you want to extend a built-in class you need it's class ID and there
is no robust way to get that without this accessor.

* add JS_INVALID_CLASS_ID constant for invalid class ID.

Signed-off-by: Tyler Rockwood <[email protected]>

Author: rockwotj

quickjs.c

@@ -3391,6 +3391,15 @@ JSClassID JS_NewClassID(JSClassID *pclass_id)
     return class_id;
 }
 
+JSClassID JS_GetClassID(JSValue v)
+{
+    JSObject *p;
+    if (JS_VALUE_GET_TAG(v) != JS_TAG_OBJECT)
+        return JS_INVALID_CLASS_ID;
+    p = JS_VALUE_GET_OBJ(v);
+    return p->class_id;
+}
+
 BOOL JS_IsRegisteredClass(JSRuntime *rt, JSClassID class_id)
 {
     return (class_id < rt->class_count &&

quickjs.h

@@ -499,7 +499,10 @@ typedef struct JSClassDef {
     JSClassExoticMethods *exotic;
 } JSClassDef;
 
+#define JS_INVALID_CLASS_ID 0
 JSClassID JS_NewClassID(JSClassID *pclass_id);
+/* Returns the class ID if `v` is an object, otherwise returns JS_INVALID_CLASS_ID. */
+JSClassID JS_GetClassID(JSValue v);
 int JS_NewClass(JSRuntime *rt, JSClassID class_id, const JSClassDef *class_def);
 int JS_IsRegisteredClass(JSRuntime *rt, JSClassID class_id);