js-sys: Add bindings for WebAssembly.instantiateStreaming

Part of #275

crates/js-sys/src/lib.rs

@@ -2880,6 +2880,15 @@ pub mod WebAssembly {
         #[wasm_bindgen(js_namespace = WebAssembly, js_name = instantiate)]
         pub fn instantiate_module(module: &Module, imports: &Object) -> Promise;
 
+        /// The `WebAssembly.instantiateStreaming()` function compiles and
+        /// instantiates a WebAssembly module directly from a streamed
+        /// underlying source. This is the most efficient, optimized way to load
+        /// wasm code.
+        ///
+        /// [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/instantiateStreaming)
+        #[wasm_bindgen(js_namespace = WebAssembly, js_name = instantiateStreaming)]
+        pub fn instantiate_streaming(response: &Promise, imports: &Object) -> Promise;
+
         /// The `WebAssembly.validate()` function validates a given typed
         /// array of WebAssembly binary code, returning whether the bytes
         /// form a valid wasm module (`true`) or not (`false`).

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

@@ -31,6 +31,12 @@ function getImports() {
   };
 }
 
+// Polyfill `WebAssembly.instantiateStreaming` for node.
+if (!global.WebAssembly.instantiateStreaming) {
+  global.WebAssembly.instantiateStreaming =
+    (response, imports) => response.then(buf => WebAssembly.instantiate(buf, imports));
+}
+
 module.exports = {
   getInvalidTableObject,
   getTableObject,

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

@@ -183,6 +183,20 @@ fn instantiate_module() -> impl Future<Item = (), Error = JsValue> {
         })
 }
 
+#[wasm_bindgen_test(async)]
+fn instantiate_streaming() -> impl Future<Item = (), Error = JsValue> {
+    let response = Promise::resolve(&get_valid_wasm());
+    let imports = get_imports();
+    let p = WebAssembly::instantiate_streaming(&response, &imports);
+    JsFuture::from(p)
+        .map(|obj| {
+            assert!(
+                Reflect::get(obj.as_ref(), &"instance".into())
+                    .is_instance_of::<WebAssembly::Instance>()
+            );
+        })
+}
+
 #[wasm_bindgen_test]
 fn memory_works() {
     let obj = Object::new();