2 files changed, 45 insertions, 0 deletions
diff --git a/tests/ports/webassembly/py_proxy_dict_undefined.mjs b/tests/ports/webassembly/py_proxy_dict_undefined.mjs
new file mode 100644
index 000000000..d47a6a028
--- /dev/null
+++ b/tests/ports/webassembly/py_proxy_dict_undefined.mjs
@@ -0,0 +1,34 @@
+// Test passing a Python dict into JavaScript, how it behaves with undefined keys.
+// If JavaScript accesses a key that does not exist, `undefined` should be returned.
+// This is different to Python-side behaviour, where `KeyError` is raised.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+// Create a JavaScript function with default arguments.
+// When `value` is `undefined` it will receive its default.
+function withDefault({ value = "OK" } = {}) {
+    console.log(value);
+}
+
+globalThis.withDefault = withDefault;
+
+// Call the function from JavaScript with various arguments.
+withDefault();
+withDefault({});
+withDefault({ value: null });
+withDefault({ value: undefined });
+withDefault({ value: () => {} });
+
+console.log("====");
+
+// Call the function from Python with the same arguments as above.
+// The results should be the same.
+mp.runPython(`
+import js
+
+js.withDefault()
+js.withDefault({})
+js.withDefault({"value": None})
+js.withDefault({"value": js.undefined})
+js.withDefault({"value": (lambda: {})})
+`);
diff --git a/tests/ports/webassembly/py_proxy_dict_undefined.mjs.exp b/tests/ports/webassembly/py_proxy_dict_undefined.mjs.exp
new file mode 100644
index 000000000..6cf5b9fa1
--- /dev/null
+++ b/tests/ports/webassembly/py_proxy_dict_undefined.mjs.exp
@@ -0,0 +1,11 @@
+OK
+OK
+null
+OK
+[Function: value]
+====
+OK
+OK
+null
+OK
+[Function: obj] { _ref: 7 }