Use proper duck typing for JsProxy (#1186)

packages/micropip/micropip/micropip.py

@@ -12,7 +12,10 @@ except ImportError:
 
         class _module:
             class packages:
-                dependencies = []  # type: ignore
+                class dependencies:
+                    @staticmethod
+                    def object_entries():
+                        return []
 
 
 import hashlib
@@ -140,7 +143,9 @@ class _PackageManager:
 
     def __init__(self):
         self.builtin_packages = {}
-        self.builtin_packages.update(js_pyodide._module.packages.dependencies)
+        self.builtin_packages.update(
+            js_pyodide._module.packages.dependencies.object_entries()
+        )
         self.installed_packages = {}
 
     def install(

src/core/hiwire.c

@@ -6,6 +6,9 @@
 
 #include "hiwire.h"
 
+#define ERROR_REF (0)
+#define ERROR_NUM (-1)
+
 const JsRef Js_undefined = ((JsRef)(2));
 const JsRef Js_true = ((JsRef)(4));
 const JsRef Js_false = ((JsRef)(6));
@@ -217,6 +220,18 @@ EM_JS(void _Py_NO_RETURN, hiwire_throw_error, (JsRef iderr), {
   throw Module.hiwire.pop_value(iderr);
 });
 
+EM_JS_NUM(bool, hiwire_is_array, (JsRef idobj), {
+  let obj = Module.hiwire.get_value(idobj);
+  if (Array.isArray(obj)) {
+    return true;
+  }
+  let result = Object.prototype.toString.call(obj);
+  // We want to treat some standard array-like objects as Array.
+  // clang-format off
+  return result === "[object HTMLCollection]" || result === "[object NodeList]";
+  // clang-format on
+});
+
 EM_JS_REF(JsRef, hiwire_array, (), { return Module.hiwire.new_value([]); });
 
 EM_JS_NUM(errcode, hiwire_push_array, (JsRef idarr, JsRef idval), {
@@ -237,21 +252,25 @@ EM_JS_NUM(errcode,
 
 EM_JS_REF(JsRef, hiwire_get_global, (const char* ptrname), {
   let jsname = UTF8ToString(ptrname);
-  if (jsname in self) {
-    return Module.hiwire.new_value(self[jsname]);
-  } else {
-    return Module.hiwire.ERROR;
+  let result = globalThis[jsname];
+  // clang-format off
+  if (result === undefined && !(jsname in globalThis)) {
+    // clang-format on
+    return ERROR_REF;
   }
+  return Module.hiwire.new_value(result);
 });
 
 EM_JS_REF(JsRef, hiwire_get_member_string, (JsRef idobj, const char* ptrkey), {
   let jsobj = Module.hiwire.get_value(idobj);
   let jskey = UTF8ToString(ptrkey);
-  if (jskey in jsobj) {
-    return Module.hiwire.new_value(jsobj[jskey]);
-  } else {
-    return Module.hiwire.ERROR;
+  let result = jsobj[jskey];
+  // clang-format off
+  if (result === undefined && !(jskey in jsobj)) {
+    // clang-format on
+    return ERROR_REF;
   }
+  return Module.hiwire.new_value(result);
 });
 
 EM_JS_NUM(errcode,
@@ -274,22 +293,40 @@ EM_JS_NUM(errcode,
           });
 
 EM_JS_REF(JsRef, hiwire_get_member_int, (JsRef idobj, int idx), {
-  let jsobj = Module.hiwire.get_value(idobj);
-  return Module.hiwire.new_value(jsobj[idx]);
+  let obj = Module.hiwire.get_value(idobj);
+  let result = obj[idx];
+  // clang-format off
+  if (result === undefined && !(idx in obj)) {
+    // clang-format on
+    return ERROR_REF;
+  }
+  return Module.hiwire.new_value(result);
 });
 
 EM_JS_NUM(errcode, hiwire_set_member_int, (JsRef idobj, int idx, JsRef idval), {
   Module.hiwire.get_value(idobj)[idx] = Module.hiwire.get_value(idval);
 });
 
+EM_JS_NUM(errcode, hiwire_delete_member_int, (JsRef idobj, int idx), {
+  let obj = Module.hiwire.get_value(idobj);
+  // Weird edge case: allow deleting an empty entry, but we raise a key error if
+  // access is attempted.
+  if (idx < 0 || idx >= obj.length) {
+    return ERROR_NUM;
+  }
+  obj.splice(idx, 1);
+});
+
 EM_JS_REF(JsRef, hiwire_get_member_obj, (JsRef idobj, JsRef ididx), {
   let jsobj = Module.hiwire.get_value(idobj);
   let jsidx = Module.hiwire.get_value(ididx);
-  if (jsidx in jsobj) {
-    return Module.hiwire.new_value(jsobj[jsidx]);
-  } else {
-    return Module.hiwire.ERROR;
+  let result = jsobj[jsidx];
+  // clang-format off
+  if (result === undefined && !(jsidx in jsobj)) {
+    // clang-format on
+    return ERROR_REF;
   }
+  return Module.hiwire.new_value(result);
 });
 
 EM_JS_NUM(errcode,
@@ -362,8 +399,25 @@ EM_JS_REF(JsRef, hiwire_new, (JsRef idobj, JsRef idargs), {
   return Module.hiwire.new_value(Reflect.construct(jsobj, jsargs));
 });
 
+EM_JS_NUM(bool, hiwire_has_length, (JsRef idobj), {
+  let val = Module.hiwire.get_value(idobj);
+  // clang-format off
+  return (typeof val.size === "number") ||
+         (typeof val.length === "number" && typeof val !== "function");
+  // clang-format on
+});
+
 EM_JS_NUM(int, hiwire_get_length, (JsRef idobj), {
-  return Module.hiwire.get_value(idobj).length;
+  let val = Module.hiwire.get_value(idobj);
+  // clang-format off
+  if (typeof val.size === "number") {
+    return val.size;
+  }
+  if (typeof val.length === "number") {
+    return val.length;
+  }
+  // clang-format on
+  return ERROR_NUM;
 });
 
 EM_JS_NUM(bool, hiwire_get_bool, (JsRef idobj), {
@@ -383,12 +437,88 @@ EM_JS_NUM(bool, hiwire_get_bool, (JsRef idobj), {
   // clang-format on
 });
 
-EM_JS_NUM(bool, hiwire_is_pyproxy, (JsRef idobj), {
+EM_JS_NUM(bool, hiwire_has_has_method, (JsRef idobj), {
   // clang-format off
-  return Module.PyProxy.isPyProxy(Module.hiwire.get_value(idobj));
+  let obj = Module.hiwire.get_value(idobj);
+  return obj && typeof obj.has === "function";
   // clang-format on
 });
 
+EM_JS_NUM(bool, hiwire_call_has_method, (JsRef idobj, JsRef idkey), {
+  // clang-format off
+  let obj = Module.hiwire.get_value(idobj);
+  let key = Module.hiwire.get_value(idkey);
+  return obj.has(key);
+  // clang-format on
+});
+
+EM_JS_NUM(bool, hiwire_has_includes_method, (JsRef idobj), {
+  // clang-format off
+  let obj = Module.hiwire.get_value(idobj);
+  return obj && typeof obj.includes === "function";
+  // clang-format on
+});
+
+EM_JS_NUM(bool, hiwire_call_includes_method, (JsRef idobj, JsRef idval), {
+  let obj = Module.hiwire.get_value(idobj);
+  let val = Module.hiwire.get_value(idval);
+  return obj.includes(val);
+});
+
+EM_JS_NUM(bool, hiwire_has_get_method, (JsRef idobj), {
+  // clang-format off
+  let obj = Module.hiwire.get_value(idobj);
+  return obj && typeof obj.get === "function";
+  // clang-format on
+});
+
+EM_JS_REF(JsRef, hiwire_call_get_method, (JsRef idobj, JsRef idkey), {
+  let obj = Module.hiwire.get_value(idobj);
+  let key = Module.hiwire.get_value(idkey);
+  let result = obj.get(key);
+  // clang-format off
+  if (result === undefined) {
+    // Try to distinguish between undefined and missing:
+    // If the object has a "has" method and it returns false for this key, the
+    // key is missing. Otherwise, assume key present and value was undefined.
+    // TODO: in absence of a "has" method, should we return None or KeyError?
+    if (obj.has && typeof obj.has === "function" && !obj.has(key)) {
+      return ERROR_REF;
+    }
+  }
+  // clang-format on
+  return Module.hiwire.new_value(result);
+});
+
+EM_JS_NUM(bool, hiwire_has_set_method, (JsRef idobj), {
+  // clang-format off
+  let obj = Module.hiwire.get_value(idobj);
+  return obj && typeof obj.set === "function";
+  // clang-format on
+});
+
+EM_JS_NUM(errcode,
+          hiwire_call_set_method,
+          (JsRef idobj, JsRef idkey, JsRef idval),
+          {
+            let obj = Module.hiwire.get_value(idobj);
+            let key = Module.hiwire.get_value(idkey);
+            let val = Module.hiwire.get_value(idval);
+            let result = obj.set(key, val);
+          });
+
+EM_JS_NUM(errcode, hiwire_call_delete_method, (JsRef idobj, JsRef idkey), {
+  let obj = Module.hiwire.get_value(idobj);
+  let key = Module.hiwire.get_value(idkey);
+  if (!obj.delete(key)) {
+    return -1;
+  }
+});
+
+EM_JS_NUM(bool, hiwire_is_pyproxy, (JsRef idobj), {
+  return Module.PyProxy.isPyProxy(Module.hiwire.get_value(idobj));
+});
+
 EM_JS_NUM(bool, hiwire_is_function, (JsRef idobj), {
   // clang-format off
   return typeof Module.hiwire.get_value(idobj) === 'function';
@@ -448,34 +578,40 @@ MAKE_OPERATOR(not_equal, !==);
 MAKE_OPERATOR(greater_than, >);
 MAKE_OPERATOR(greater_than_equal, >=);
 
-EM_JS_REF(int, hiwire_next, (JsRef idobj, JsRef* result_ptr), {
-  // clang-format off
+EM_JS_REF(JsRef, hiwire_is_iterator, (JsRef idobj), {
   let jsobj = Module.hiwire.get_value(idobj);
+  // clang-format off
+  return typeof jsobj.next === 'function';
+  // clang-format on
+});
+
+EM_JS_NUM(int, hiwire_next, (JsRef idobj, JsRef* result_ptr), {
+  let jsobj = Module.hiwire.get_value(idobj);
+  // clang-format off
   let { done, value } = jsobj.next();
+  // clang-format on
   let result_id = Module.hiwire.new_value(value);
   setValue(result_ptr, result_id, "i32");
   return done;
+});
+
+EM_JS_REF(JsRef, hiwire_is_iterable, (JsRef idobj), {
+  let jsobj = Module.hiwire.get_value(idobj);
+  // clang-format off
+  return typeof jsobj[Symbol.iterator] === 'function';
   // clang-format on
 });
 
 EM_JS_REF(JsRef, hiwire_get_iterator, (JsRef idobj), {
-  // clang-format off
-  if (idobj === Module.hiwire.UNDEFINED) {
-    return Module.hiwire.ERROR;
-  }
-
   let jsobj = Module.hiwire.get_value(idobj);
-  if (typeof jsobj.next === 'function') {
-    return Module.hiwire.new_value(jsobj);
-  } else if (typeof jsobj[Symbol.iterator] === 'function') {
-    return Module.hiwire.new_value(jsobj[Symbol.iterator]());
-  } else {
-    return Module.hiwire.new_value(Object.entries(jsobj)[Symbol.iterator]());
-  }
-  return Module.hiwire.ERROR;
-  // clang-format on
+  return Module.hiwire.new_value(jsobj[Symbol.iterator]());
 })
 
+EM_JS_REF(JsRef, hiwire_object_entries, (JsRef idobj), {
+  let jsobj = Module.hiwire.get_value(idobj);
+  return Module.hiwire.new_value(Object.entries(jsobj));
+});
+
 EM_JS_NUM(bool, hiwire_is_typedarray, (JsRef idobj), {
   let jsobj = Module.hiwire.get_value(idobj);
   // clang-format off
@@ -541,7 +677,7 @@ EM_JS_REF(JsRef, hiwire_subarray, (JsRef idarr, int start, int end), {
   return Module.hiwire.new_value(jssub);
 });
 
-EM_JS_NUM(JsRef, JsMap_New, (), { return Module.hiwire.new_value(new Map()); })
+EM_JS_REF(JsRef, JsMap_New, (), { return Module.hiwire.new_value(new Map()); })
 
 EM_JS_NUM(errcode, JsMap_Set, (JsRef mapid, JsRef keyid, JsRef valueid), {
   let map = Module.hiwire.get_value(mapid);
@@ -550,7 +686,7 @@ EM_JS_NUM(errcode, JsMap_Set, (JsRef mapid, JsRef keyid, JsRef valueid), {
   map.set(key, value);
 })
 
-EM_JS_NUM(JsRef, JsSet_New, (), { return Module.hiwire.new_value(new Set()); })
+EM_JS_REF(JsRef, JsSet_New, (), { return Module.hiwire.new_value(new Set()); })
 
 EM_JS_NUM(errcode, JsSet_Add, (JsRef mapid, JsRef keyid), {
   let set = Module.hiwire.get_value(mapid);

src/core/hiwire.h

@@ -240,6 +240,9 @@ hiwire_float64array(f64* ptr, int len);
 JsRef
 hiwire_bool(bool boolean);
 
+bool
+hiwire_is_array(JsRef idobj);
+
 /**
  * Create a new Javascript Array.
  *
@@ -306,7 +309,6 @@ hiwire_set_member_string(JsRef idobj, const char* ptrname, JsRef idval);
 
 /**
  * Delete an object member by string.
- *
  */
 errcode
 hiwire_delete_member_string(JsRef idobj, const char* ptrname);
@@ -314,8 +316,6 @@ hiwire_delete_member_string(JsRef idobj, const char* ptrname);
 /**
  * Get an object member by integer.
  *
- * The integer is a C integer, not an id reference to a Javascript integer.
- *
  * Returns: New reference
  */
 JsRef
@@ -323,13 +323,13 @@ hiwire_get_member_int(JsRef idobj, int idx);
 
 /**
  * Set an object member by integer.
- *
- * The integer is a C integer, not an id reference to a Javascript integer.
- *
  */
 errcode
 hiwire_set_member_int(JsRef idobj, int idx, JsRef idval);
 
+errcode
+hiwire_delete_member_int(JsRef idobj, int idx);
+
 /**
  * Get an object member by object.
  *
@@ -398,35 +398,112 @@ JsRef
 hiwire_new(JsRef idobj, JsRef idargs);
 
 /**
- * Returns the value of the `length` member on a Javascript object.
- *
- * Returns: C int
+ * Test if the object has a `size` or `length` member which is a number. As a
+ * special case, if the object is a function the `length` field is ignored.
+ */
+bool
+hiwire_has_length(JsRef idobj);
+
+/**
+ * Returns the value of the `size` or `length` member on a Javascript object.
+ * Prefers the `size` member if present and a number to the `length` field. If
+ * both `size` and `length` are missing or not a number, returns `-1` to
+ * indicate error.
  */
 int
 hiwire_get_length(JsRef idobj);
 
 /**
  * Returns the boolean value of a Javascript object.
- *
- * Returns: C int
  */
 bool
 hiwire_get_bool(JsRef idobj);
 
+/**
+ * Check whether `typeof obj.has === "function"`
+ */
+bool
+hiwire_has_has_method(JsRef idobj);
+
+/**
+ * Does `obj.has(val)`. Doesn't check type of return value, if it isn't a
+ * boolean or an integer it will get coerced to false.
+ */
+bool
+hiwire_call_has_method(JsRef idobj, JsRef idval);
+
+/**
+ * Check whether `typeof obj.includes === "function"`.
+ */
+bool
+hiwire_has_includes_method(JsRef idobj);
+
+/**
+ * Does `obj.includes(val)`. Doesn't check type of return value, if it isn't a
+ * boolean or an integer it will get coerced to `false`.
+ */
+bool
+hiwire_call_includes_method(JsRef idobj, JsRef idval);
+
+/**
+ * Check whether `typeof obj.get === "function"`.
+ */
+bool
+hiwire_has_get_method(JsRef idobj);
+
+/**
+ * Call `obj.get(key)`. If the result is `undefined`, we check for a `has`
+ * method and if one is present call `obj.has(key)`. If this returns false we
+ * return `NULL` to signal a `KeyError` otherwise we return `Js_Undefined`. If
+ * no `has` method is present, we return `Js_Undefined`.
+ */
+JsRef
+hiwire_call_get_method(JsRef idobj, JsRef idkey);
+
+/**
+ * Check whether `typeof obj.set === "function"`.
+ */
+bool
+hiwire_has_set_method(JsRef idobj);
+
+/**
+ * Call `obj.set(key, value)`. Javascript standard is that `set` returns `false`
+ * to indicate an error condition, but we ignore the return value.
+ */
+errcode
+hiwire_call_set_method(JsRef idobj, JsRef idkey, JsRef idval);
+
+/**
+ * Call `obj.delete(key)`. Javascript standard is that `delete` returns `false`
+ * to indicate an error condition, if `false` is returned we return `-1` to
+ * indicate the error.
+ */
+errcode
+hiwire_call_delete_method(JsRef idobj, JsRef idkey);
+
+/**
+ * Check whether the object is a PyProxy.
+ */
 bool
 hiwire_is_pyproxy(JsRef idobj);
 
 /**
- * Returns 1 if the object is a function.
- *
- * Returns: C int
+ * Check if the object is a function.
  */
 bool
 hiwire_is_function(JsRef idobj);
 
+/**
+ * Check if the object is an error.
+ */
 bool
 hiwire_is_error(JsRef idobj);
 
+/**
+ * Check if the function supports kwargs. A fairly involved check which parses
+ * func.toString() to determine if the last argument does object destructuring.
+ * Actual implementation in pyodide.js.
+ */
 bool
 hiwire_function_supports_kwargs(JsRef idfunc);
 
@@ -453,7 +530,7 @@ JsRef
 hiwire_to_string(JsRef idobj);
 
 /**
- * Gets the "typeof" string for a value.
+ * Gets the `typeof` string for a value.
  *
  * Returns: New reference to Javascript string
  */
@@ -461,7 +538,7 @@ JsRef
 hiwire_typeof(JsRef idobj);
 
 /**
- * Gets "value.constructor.name".
+ * Gets `value.constructor.name`.
  *
  * Returns: New reference to Javascript string
  */
@@ -504,21 +581,40 @@ hiwire_greater_than(JsRef ida, JsRef idb);
 bool
 hiwire_greater_than_equal(JsRef ida, JsRef idb);
 
+/**
+ * Check if `typeof obj.next === "function"`
+ */
+JsRef
+hiwire_is_iterator(JsRef idobj);
+
 /**
  * Calls the `next` function on an iterator.
  *
- * Returns -1 if an error occurs.
- * Stores "value" into argument "result", returns "done".
+ * Returns -1 if an error occurs. Otherwise, `next` should return an object with
+ * `value` and `done` fields. We store `value` into the argument `result` and
+ * return `done`.
  */
 int
 hiwire_next(JsRef idobj, JsRef* result);
 
+/**
+ * Check if `typeof obj[Symbol.iterator] === "function"`
+ */
+JsRef
+hiwire_is_iterable(JsRef idobj);
+
 /**
  * Returns the iterator associated with the given object, if any.
  */
 JsRef
 hiwire_get_iterator(JsRef idobj);
 
+/**
+ * Returns `Object.entries(obj)`
+ */
+JsRef
+hiwire_object_entries(JsRef idobj);
+
 /**
  * Returns 1 if the value is a typedarray.
  */
@@ -532,10 +628,10 @@ bool
 hiwire_is_on_wasm_heap(JsRef idobj);
 
 /**
- * Returns the value of obj.byteLength.
+ * Returns the value of `obj.byteLength`.
  *
  * There is no error checking. Caller must ensure that hiwire_is_typedarray is
- * true.
+ * true. If these conditions are not met, returns `0`.
  */
 int
 hiwire_get_byteLength(JsRef idobj);
@@ -544,7 +640,8 @@ hiwire_get_byteLength(JsRef idobj);
  * Returns the value of obj.byteOffset.
  *
  * There is no error checking. Caller must ensure that hiwire_is_typedarray is
- * true and hiwire_is_on_wasm_heap is true.
+ * true and hiwire_is_on_wasm_heap is true. If these conditions are not met,
+ * returns `0`.
  */
 int
 hiwire_get_byteOffset(JsRef idobj);
@@ -568,15 +665,27 @@ hiwire_get_dtype(JsRef idobj, char** format_ptr, Py_ssize_t* size_ptr);
 JsRef
 hiwire_subarray(JsRef idarr, int start, int end);
 
+/**
+ * Create a new Map.
+ */
 JsRef
 JsMap_New();
 
+/**
+ * Does map.set(key, value).
+ */
 errcode
 JsMap_Set(JsRef mapid, JsRef keyid, JsRef valueid);
 
+/**
+ * Create a new Set.
+ */
 JsRef
 JsSet_New();
 
+/**
+ * Does set.add(key).
+ */
 errcode
 JsSet_Add(JsRef mapid, JsRef keyid);
 

src/core/js2python.c

@@ -61,6 +61,9 @@ PyObject*
 _js2python_memoryview(JsRef id)
 {
   PyObject* jsproxy = JsProxy_create(id);
+  if (jsproxy == NULL) {
+    return NULL;
+  }
   return PyMemoryView_FromObject(jsproxy);
 }
 

src/core/jsproxy.h

@@ -17,6 +17,9 @@
 PyObject*
 JsProxy_create(JsRef v);
 
+PyObject*
+JsProxy_create_with_this(JsRef object, JsRef this);
+
 /** Check if a Python object is a JsProxy object.
  *  \param x The Python object
  *  \return true if the object is a JsProxy object.

src/core/python2js.c

@@ -231,7 +231,8 @@ _python2js_bytes(PyObject* x)
 // and PySequence_Check returns 1 for classes with a __getitem__ method that
 // don't subclass dict. For this reason, I think we should stick to subclasses.
 
-/** WARNING: This function is not suitable for fallbacks. If this function
+/**
+ * WARNING: This function is not suitable for fallbacks. If this function
  * returns NULL, we must assume that the cache has been corrupted and bail out.
  */
 static JsRef
@@ -266,7 +267,8 @@ finally:
   return jsarray;
 }
 
-/** WARNING: This function is not suitable for fallbacks. If this function
+/**
+ * WARNING: This function is not suitable for fallbacks. If this function
  * returns NULL, we must assume that the cache has been corrupted and bail out.
  */
 static JsRef

src/pyodide-py/pyodide/_core.py

@@ -2,7 +2,7 @@
 import platform
 
 if platform.system() == "Emscripten":
-    from _pyodide_core import JsProxy, JsMethod, JsException, JsBuffer
+    from _pyodide_core import JsProxy, JsException, JsBuffer
 else:
     # Can add shims here if we are so inclined.
     class JsException(Exception):
@@ -17,15 +17,10 @@ else:
 
         # Defined in jsproxy.c
 
-    class JsMethod:
-        """A proxy to make it possible to call Javascript bound methods from Python."""
-
-        # Defined in jsproxy.c
-
     class JsBuffer:
         """A proxy to make it possible to call Javascript typed arrays from Python."""
 
         # Defined in jsproxy.c
 
 
-__all__ = [JsProxy, JsMethod, JsException]
+__all__ = [JsProxy, JsException]

src/tests/test_jsproxy.py

@@ -22,7 +22,6 @@ def test_jsproxy_dir(selenium):
             "__defineGetter__",
             "__defineSetter__",
             "__delattr__",
-            "__delitem__",
             "constructor",
             "toString",
             "typeof",
@@ -88,28 +87,25 @@ def test_jsproxy(selenium):
     assert (
         selenium.run(
             """
-        from js import TEST
-        del TEST.y
-        hasattr(TEST, 'y')"""
+            from js import TEST
+            del TEST.y
+            hasattr(TEST, 'y')
+            """
         )
         is False
     )
     selenium.run_js(
         """
-        class Point {
-          constructor(x, y) {
-            this.x = x;
-            this.y = y;
-          }
-        }
-        window.TEST = new Point(42, 43);"""
+        window.TEST = new Map([["x", 42], ["y", 43]]);
+        """
     )
     assert (
         selenium.run(
             """
-        from js import TEST
-        del TEST['y']
-        'y' in TEST"""
+            from js import TEST
+            del TEST['y']
+            'y' in TEST
+            """
         )
         is False
     )
@@ -134,7 +130,7 @@ def test_jsproxy(selenium):
         selenium.run(
             """
         from js import TEST
-        dict(TEST) == {'foo': 'bar', 'baz': 'bap'}
+        dict(TEST.object_entries()) == {'foo': 'bar', 'baz': 'bap'}
         """
         )
         is True
@@ -440,12 +436,11 @@ def test_unregister_jsmodule(selenium):
         pyodide.registerJsModule("a", a);
         pyodide.registerJsModule("a", b);
         pyodide.unregisterJsModule("a")
-        pyodide.runPython(`
-            try:
+        await pyodide.runPythonAsync(`
+            from unittest import TestCase
+            raises = TestCase().assertRaises
+            with raises(ImportError):
                 import a
-                assert False
-            except ImportError:
-                pass
         `)
         """
     )
@@ -508,3 +503,214 @@ def test_register_jsmodule_docs_example(selenium):
         assert c == 2
         """
     )
+
+
+def test_mixins_feature_presence(selenium):
+    result = selenium.run_js(
+        """
+        let fields = [
+            [{ [Symbol.iterator](){} }, "__iter__"],
+            [{ next(){} }, "__next__", "__iter__"],
+            [{ length : 1 }, "__len__"],
+            [{ get(){} }, "__getitem__"],
+            [{ set(){} }, "__setitem__", "__delitem__"],
+            [{ has(){} }, "__contains__"],
+            [{ then(){} }, "__await__"]
+        ];
+        
+        let test_object = pyodide.runPython(`
+            from js import console
+            def test_object(obj, keys_expected):
+                for [key, expected_val] in keys_expected.object_entries():
+                    actual_val = hasattr(obj, key)
+                    if actual_val != expected_val:
+                        console.log(obj)
+                        console.log(key)
+                        console.log(actual_val)
+                        assert False
+            test_object
+        `);
+
+        for(let flags = 0; flags < (1 << fields.length); flags ++){
+            let o = {};
+            let keys_expected = {};
+            for(let [idx, [obj, ...keys]] of fields.entries()){
+                if(flags & (1<<idx)){
+                    Object.assign(o, obj);
+                }
+                for(let key of keys){
+                    keys_expected[key] = keys_expected[key] || !!(flags & (1<<idx));
+                }
+            }
+            test_object(o, keys_expected);
+        }
+        """
+    )
+
+
+def test_mixins_calls(selenium):
+    result = selenium.run_js(
+        """
+        window.testObjects = {};
+        testObjects.iterable = { *[Symbol.iterator](){
+            yield 3; yield 5; yield 7;
+        } };
+        testObjects.iterator = testObjects.iterable[Symbol.iterator]();
+        testObjects.has_len1 = { length : 7, size : 10 };
+        testObjects.has_len2 = { length : 7 };
+        testObjects.has_get = { get(x){ return x; } };
+        testObjects.has_getset = new Map();
+        testObjects.has_has = { has(x){ return typeof(x) === "string" && x.startsWith("x") } };
+        testObjects.has_includes = { includes(x){ return typeof(x) === "string" && x.startsWith("a") } };
+        testObjects.has_has_includes = { 
+            includes(x){ return typeof(x) === "string" && x.startsWith("a") },
+            has(x){ return typeof(x) === "string" && x.startsWith("x") }
+        };
+        testObjects.awaitable = { then(cb){ cb(7); } };
+
+        let result = await pyodide.runPythonAsync(`
+            from js import testObjects as obj
+            result = []
+            result.append(["iterable1", list(iter(obj.iterable)), [3, 5, 7]])
+            result.append(["iterable2", [*obj.iterable], [3, 5, 7]])
+            it = obj.iterator
+            result.append(["iterator", [next(it), next(it), next(it)], [3, 5, 7]])
+            result.append(["has_len1", len(obj.has_len1), 10])
+            result.append(["has_len2", len(obj.has_len2), 7])
+            result.append(["has_get1", obj.has_get[10], 10])
+            result.append(["has_get2", obj.has_get[11], 11])
+            m = obj.has_getset
+            m[1] = 6
+            m[2] = 77
+            m[3] = 9
+            m[2] = 5
+            del m[3]
+            result.append(["has_getset", [x.to_py() for x in m.entries()], [[1, 6], [2, 5]]])
+            result.append(["has_has", [n in obj.has_has for n in ["x9", "a9"]], [True, False]])
+            result.append(["has_includes", [n in obj.has_includes for n in ["x9", "a9"]], [False, True]])
+            result.append(["has_has_includes", [n in obj.has_has_includes for n in ["x9", "a9"]], [True, False]])
+            result.append(["awaitable", await obj.awaitable, 7])
+            result
+        `);
+        return result.toJs();
+        """
+    )
+    for [desc, a, b] in result:
+        assert a == b, desc
+
+
+def test_mixins_errors(selenium):
+    selenium.run_js(
+        """
+        window.a = [];
+        window.b = { 
+            has(){ return false; },
+            get(){ return undefined; },
+            set(){ return false; },
+            delete(){ return false; },
+        };
+        await pyodide.runPythonAsync(`
+            from unittest import TestCase
+            raises = TestCase().assertRaises
+            from js import a, b
+            with raises(IndexError):
+                a[0]
+            with raises(IndexError):
+                del a[0]
+            with raises(KeyError):
+                b[0]
+            with raises(KeyError):
+                del b[0]
+        `);
+
+        window.c = {
+            next(){},
+            length : 1,
+            get(){},
+            set(){},
+            has(){},
+            then(){}     
+        };
+        window.d = {
+            [Symbol.iterator](){},
+        };
+        pyodide.runPython("from js import c, d");
+        delete c.next;
+        delete c.length;
+        delete c.get;
+        delete c.set;
+        delete c.has;
+        delete c.then;
+        delete d[Symbol.iterator];
+        await pyodide.runPythonAsync(`
+            from contextlib import contextmanager
+            from unittest import TestCase
+            @contextmanager
+            def raises(exc, match=None):
+                with TestCase().assertRaisesRegex(exc, match) as e:
+                    yield e
+
+            from pyodide import JsException
+            msg = "^TypeError:.* is not a function$"
+            with raises(JsException, match=msg):
+                next(c)
+            with raises(JsException, match=msg):
+                iter(d)
+            with raises(TypeError, match="object does not have a valid length"):
+                len(c)
+            with raises(JsException, match=msg):
+                c[0]
+            with raises(JsException, match=msg):
+                c[0] = 7
+            with raises(JsException, match=msg):
+                del c[0]
+            with raises(TypeError, match="can't be used in 'await' expression"):
+                await c
+        `);
+
+        window.l = [0, false, NaN, undefined, null];
+        window.l[6] = 7;
+        await pyodide.runPythonAsync(`
+            from unittest import TestCase
+            raises = TestCase().assertRaises
+            from js import l
+            with raises(IndexError):
+                l[10]
+            with raises(IndexError):
+                l[5]
+            assert len(l) == 7
+            l[0]; l[1]; l[2]; l[3]
+            l[4]; l[6]
+            del l[1]
+            with raises(IndexError):
+                l[4]
+            l[5]
+            del l[4]
+            l[3]; l[4]
+        `);
+
+        window.l = [0, false, NaN, undefined, null];
+        window.l[6] = 7;
+        let a = Array.from(window.l.entries());
+        console.log(a);
+        a.splice(5, 1);
+        window.m = new Map(a);
+        console.log(m.size);
+        await pyodide.runPythonAsync(`
+            from js import m
+            from unittest import TestCase
+            raises = TestCase().assertRaises
+            with raises(KeyError):
+                m[10]
+            with raises(KeyError):
+                m[5]
+            assert len(m) == 6
+            m[0]; m[1]; m[2]; m[3]
+            m[4]; m[6]
+            del m[1]
+            with raises(KeyError):
+                m[1]
+            assert len(m) == 5
+        `);
+        """
+    )

src/tests/test_pyodide.py

@@ -182,10 +182,12 @@ def test_hiwire_is_promise(selenium):
         "new Map()",
         "new Set()",
     ]:
-        assert not selenium.run_js(f"return pyodide._module.hiwire.isPromise({s})")
+        assert selenium.run_js(
+            f"return pyodide._module.hiwire.isPromise({s}) === false;"
+        )
 
     assert selenium.run_js(
-        "return pyodide._module.hiwire.isPromise(Promise.resolve());"
+        "return pyodide._module.hiwire.isPromise(Promise.resolve()) === true;"
     )
 
     assert selenium.run_js(

src/tests/test_python.py

@@ -158,12 +158,12 @@ def test_eval_nothing(selenium):
 
 
 def test_unknown_attribute(selenium):
-    selenium.run(
+    selenium.run_async(
         """
+        from unittest import TestCase
+        raises = TestCase().assertRaisesRegex
         import js
-        try:
+        with raises(AttributeError, "asdf"):
             js.asdf
-        except AttributeError as e:
-            assert "asdf" in str(e)
         """
     )

src/tests/test_webloop.py

@@ -55,6 +55,8 @@ def test_capture_exception(selenium):
     run_with_resolve(
         selenium,
         """
+        from unittest import TestCase
+        raises = TestCase().assertRaises
         from js import resolve
         class MyException(Exception):
             pass
@@ -62,12 +64,9 @@ def test_capture_exception(selenium):
             raise MyException('oops')
         
         def capture_exception(fut):
-            try:
+            with raises(MyException):
                 fut.result()
-            except MyException:
-                resolve()
-            else:
-                raise Exception("Expected fut.result() to raise MyException")
+            resolve()
         import asyncio
         fut = asyncio.ensure_future(foo(998))
         fut.add_done_callback(capture_exception)                
@@ -131,16 +130,15 @@ def test_asyncio_exception(selenium):
     run_with_resolve(
         selenium,
         """
+        from unittest import TestCase
+        raises = TestCase().assertRaises
         from js import resolve
         async def dummy_task():
             raise ValueError("oops!")
         async def capture_exception():
-            try:
+            with raises(ValueError):
                 await dummy_task()
-            except ValueError:
-                resolve()
-            else:
-                raise Exception("Expected ValueError")
+            resolve()
         import asyncio
         asyncio.ensure_future(capture_exception())
         """,