js-sys: Add exports getter to WebAssembly.Instance

Part of rustwasm#275

crates/js-sys/src/lib.rs

@@ -2917,6 +2917,15 @@ pub mod WebAssembly {
         /// [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance)
         #[wasm_bindgen(catch, constructor, js_namespace = WebAssembly)]
         pub fn new(module: &Module, imports: &Object) -> Result<Instance, JsValue>;
+
+        /// The `exports` readonly property of the `WebAssembly.Instance` object
+        /// prototype returns an object containing as its members all the
+        /// functions exported from the WebAssembly module instance, to allow
+        /// them to be accessed and used by JavaScript.
+        ///
+        /// [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance/exports)
+        #[wasm_bindgen(getter, method, js_namespace = WebAssembly)]
+        pub fn exports(this: &Instance) -> Object;
     }
 
     // WebAssembly.LinkError

crates/js-sys/tests/wasm/WebAssembly.rs

@@ -157,13 +157,19 @@ fn runtime_error_inheritance() {
 }
 
 #[wasm_bindgen_test]
-fn instance_constructor_and_inheritance() {
+fn webassembly_instance() {
     let module = WebAssembly::Module::new(&get_valid_wasm()).unwrap();
     let imports = get_imports();
     let instance = WebAssembly::Instance::new(&module, &imports).unwrap();
+
+    // Inheritance chain is correct.
     assert!(instance.is_instance_of::<WebAssembly::Instance>());
     assert!(instance.is_instance_of::<Object>());
     let _: &Object = instance.as_ref();
+
+    // Has expected exports.
+    let exports = instance.exports();
+    assert!(Reflect::has(exports.as_ref(), &"exported_func".into()));
 }
 
 #[wasm_bindgen_test]