wasm: enable JSPI

guybedford · guybedford · commit 4396cf2d45f0 · 2025-09-22T18:12:43.000-07:00
PR-URL: #59941 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
diff --git a/src/node.cc b/src/node.cc
@@ -782,6 +782,9 @@ static ExitCode ProcessGlobalArgsInternal(std::vector<std::string>* args,
 
   v8_args.emplace_back("--js-source-phase-imports");
 
+  // WebAssembly JS Promise Integration
+  v8_args.emplace_back("--experimental-wasm-jspi");
+
 #ifdef __POSIX__
   // Block SIGPROF signals when sleeping in epoll_wait/kevent/etc.  Avoids the
   // performance penalty of frequent EINTR wakeups when the profiler is running.
diff --git a/test/fixtures/wasm/jspi.wasm b/test/fixtures/wasm/jspi.wasm
diff --git a/test/parallel/test-wasm.mjs b/test/parallel/test-wasm.mjs
@@ -0,0 +1,44 @@
+import '../common/index.mjs';
+import { strictEqual } from 'node:assert';
+import { readSync } from '../common/fixtures.mjs';
+
+// Test Wasm JSPI
+{
+  const asyncImport = async (x) => {
+    await new Promise((resolve) => setTimeout(resolve, 10));
+    return x + 42;
+  };
+
+  /**
+   * wasm/jspi.wasm contains:
+   *
+   * (module
+   *   (type (;0;) (func (param i32) (result i32)))
+   *   (import "js" "async" (func $async (;0;) (type 0)))
+   *   (export "test" (func $test))
+   *   (func $test (;1;) (type 0) (param $x i32) (result i32)
+   *     local.get $x
+   *     call $async
+   *   )
+   * )
+   *
+   * Which is the JS equivalent to:
+   *
+   * import { async_ } from 'js';
+   * export function test (val) {
+   *   return async_(val);
+   * }
+   *
+   * JSPI then allows turning this sync style Wasm call into async code
+   * that suspends on the promise.
+   */
+
+  const { instance } = await WebAssembly.instantiate(readSync('wasm/jspi.wasm'), {
+    js: {
+      async: new WebAssembly.Suspending(asyncImport),
+    },
+  });
+
+  const promisingExport = WebAssembly.promising(instance.exports.test);
+  strictEqual(await promisingExport(10), 52);
+}
