feat(JSFunctionProxy): implement passing kwargs as a final argument

python/pythonmonkey/helpers.py

@@ -34,13 +34,12 @@ def new(ctor):
   newCtor = pm.eval("""'use strict'; (
 function pmNewFactory(ctor)
 {
-  return function newCtor(args) {
-    args = Array.from(args || []);
-    return new ctor(...args);
+  return function newCtor() {
+    return new ctor(...[...arguments]);
   };
 }
     )""", evalOpts)(ctor)
-  return (lambda *args: newCtor(list(args)))
+  return (lambda *args, **kwargs: newCtor(*args, **kwargs))
 
 
 def simpleUncaughtExceptionHandler(loop, context):

src/JSFunctionProxy.cc

@@ -52,6 +52,18 @@ PyObject *JSFunctionProxyMethodDefinitions::JSFunctionProxy_call(PyObject *self,
     }
   }
 
+  if (kwargs && PyDict_Size(kwargs) > 0) {
+    JS::Value jsValue = jsTypeFactory(cx, kwargs);
+    if (PyErr_Occurred()) { // Check if an exception has already been set in the flow of control
+      return NULL; // Fail-fast
+    }
+    if (!jsArgsVector.append(jsValue)) {
+      // out of memory
+      setSpiderMonkeyException(cx);
+      return NULL;
+    }
+  }
+
   JS::HandleValueArray jsArgs(jsArgsVector);
   JS::RootedValue jsReturnVal(cx);
   if (!JS_CallFunctionValue(cx, thisObj, jsFunc, jsArgs, &jsReturnVal)) {

tests/js/js2py/kwargs.simple

@@ -0,0 +1,28 @@
+/**
+ * @file        js2py/kwargs.simple
+ *              Simple test which shows that kwargs passed from python to JS end up as an additional final dict argument
+ *
+ * @author      Caleb Aikens, caikens@amd.com
+ * @date        April 2026
+ */
+'use strict';
+
+function js_func() {
+  return [...arguments];
+}
+
+python.exec(`
+def kwarg_test(js_func):
+  return js_func(1, 2, i=42, j=43)
+`);
+const kwarg_test = python.eval('kwarg_test');
+
+const [first, second, kwargs] = kwarg_test(js_func);
+
+if (first     !== 1  ||
+    second    !== 2  ||
+    kwargs.i  !== 42 ||
+    kwargs.j  !== 43) {
+
+    throw new Error('args or kwargs were not passed correctly.');
+}

tests/python/test_functions.py

@@ -119,3 +119,17 @@ def test_default_vararg_func_too_few_args():
   def f(a, b, c=42, d=43, *args):
     return [a, b, c, d, *args]
   assert [1, None, 42, 43] == pm.eval("(f) => f(1)")(f)
+
+def test_kwargs_in_js():
+  assert [1, 2, {"i": 42, "j": 43}] == pm.eval("(first, second, kwargs) => {return [first, second, kwargs]}")(1, 2, i=42, j=43)
+
+def test_kwargs_in_js_arguments_array():
+  # Note: arguments object is only available in non-arrow functions
+  assert [1, 2, {"i": 42, "j": 43}] == pm.eval("(function() {return [...arguments]})")(1, 2, i=42, j=43)
+
+def test_kwargs_pass_through():
+  def py_func(*args, **kwargs):
+    return [*args, kwargs];
+
+  # Note: kwargs passed py1->js->py2 end up in args for py2 rather than kwargs, since JS has no equivalent to kwargs
+  assert [1, 2, {"i": 42, "j": 43}, {}] == pm.eval("(py_func, ...args) => { return py_func(...args)}")(py_func, 1, 2, i=42, j=43)