Expose a "js" module and a small pyodide polyfill (#54)

* Expose as "js" module

* Pyodide polyfill

* Add test

---------

Co-authored-by: Thorsten Beier <[email protected]>

include/pyjs/pycpp/core.py

@@ -13,7 +13,7 @@ def _js_mod__getattr__(name: str) -> Any:
             raise AttributeError(f"has no attribute {name}")
         return ret
 
-    js = sys.modules["pyjs.js"] = types.ModuleType("js")
+    js = sys.modules["js"] = sys.modules["pyjs.js"] = types.ModuleType("js")
     js.__getattr__ = _js_mod__getattr__
 
     def _module_mod__getattr__(name: str) -> Any:
@@ -25,6 +25,25 @@ def _module_mod__getattr__(name: str) -> Any:
     _module = sys.modules["pyjs._module"] = types.ModuleType("_module")
     _module.__getattr__ = _module_mod__getattr__
 
+    # Expose a small pyodide polyfill
+    def _pyodide__getattr__(name: str) -> Any:
+        if name == "to_js":
+            from pyjs import to_js
+            return to_js
+
+        raise AttributeError(
+            "This is not the real Pyodide. We are providing a small Pyodide polyfill for conveniance."
+            "If you are missing an important Pyodide feature, please open an issue in https://github.com/emscripten-forge/pyjs/issues"
+        )
+
+    pyodide = sys.modules["pyodide"] = types.ModuleType("pyodide")
+    pyodide.ffi = sys.modules["pyodide.ffi"] = types.ModuleType("ffi")
+    pyodide.ffi.JsException = RuntimeError
+    pyodide.ffi.JsArray = object
+    pyodide.ffi.JsProxy = object
+    pyodide.__getattr__ = _pyodide__getattr__
+    pyodide.ffi.__getattr__ = _pyodide__getattr__
+
 
 install_submodules()
 del install_submodules

tests/tests/test_pyjs.py

@@ -1,6 +1,7 @@
 import json
 import operator
 import os
+import sys
 from types import NoneType
 import asyncio
 
@@ -36,6 +37,19 @@ def test_js_function_creation():
     assert ret == "hello_world"
 
 
+def test_pyodide_polyfill():
+    # Test imports
+    from pyodide.ffi import JsException, to_js
+    if  pyjs.to_py(pyjs._module._IS_BROWSER_MAIN_THREAD):
+        from js import console, window
+    if  pyjs.to_py(pyjs._module._IS_BROWSER_WORKER_THREAD):
+        from js import console, postMessage
+
+    with pytest.raises(AttributeError):
+        from pyodide import ffi
+        ffi.foo
+
+
 def test_create_once_callable_nullary():
     def pyfunc():
         return "hello_from_pyfunc"