diff --git a/examples/demo/build.js b/examples/demo/build.js
new file mode 100644
index 0000000..fbc497f
--- /dev/null
+++ b/examples/demo/build.js
@@ -0,0 +1,41 @@
+export function buildWasm({ types, funcs, exports }) {
+  const str = s => [s.length, ...Buffer.from(s)];
+  const section = (id, data) => [id, data.length, ...data];
+
+  return new Uint8Array([
+    0x00,
+    0x61,
+    0x73,
+    0x6d, // magic
+    0x01,
+    0x00,
+    0x00,
+    0x00, // version
+
+    ...section(0x01, [
+      // types
+      types.length,
+      ...types.flatMap(([params, results]) => [0x60, params.length, ...params, results.length, ...results])
+    ]),
+
+    ...section(0x03, [
+      // funcs -> type index
+      funcs.length,
+      ...funcs.map((_, i) => i)
+    ]),
+
+    ...section(0x07, [
+      // exports
+      exports.length,
+      ...exports.flatMap(([name, kind, idx]) => [...str(name), kind, idx])
+    ]),
+
+    ...section(0x0a, [
+      funcs.length,
+      ...funcs.flatMap(({ locals = [], body }) => {
+        const code = [locals.length, ...body, 0x0b];
+        return [code.length, ...code];
+      })
+    ])
+  ]);
+}
diff --git a/examples/demo/wasm.js b/examples/demo/wasm.js
new file mode 100644
index 0000000..b7db652
--- /dev/null
+++ b/examples/demo/wasm.js
@@ -0,0 +1,17 @@
+import { buildWasm } from './build';
+
+const i32 = 0x7f;
+const local_get = i => [0x20, i];
+const i32_add = [0x6a];
+
+const wasmBytes = buildWasm({
+  types: [[[i32, i32], [i32]]],
+  funcs: [{ body: [...local_get(0), ...local_get(1), ...i32_add] }],
+  exports: [['add', 0x00, 0]]
+});
+
+console.log(`compiled to ${wasmBytes.length} bytes\n`);
+const { instance } = await WebAssembly.instantiate(wasmBytes);
+
+console.log('add(2, 3) =', instance.exports.add(2, 3));
+console.log('add(100, 200) =', instance.exports.add(100, 200));
diff --git a/src/modules/napi.c b/src/modules/napi.c
index cb243d6..9ced3bf 100644
--- a/src/modules/napi.c
+++ b/src/modules/napi.c
@@ -1344,6 +1344,7 @@ NAPI_EXTERN napi_status NAPI_CDECL napi_get_cb_info(
     if (argv) {
       size_t ncopy = requested < info->argc ? requested : info->argc;
       if (ncopy > 0) memcpy(argv, info->argv, ncopy * sizeof(napi_value));
+      for (size_t i = ncopy; i < requested; i++) argv[i] = (napi_value)js_mkundef();
     }
     *argc = info->argc;
   }