[MODULARIZE=instance] Make output file runnable on node (#24294)

Author: sbc100

src/postamble.js

@@ -300,6 +300,8 @@ function preInit() {
 }
 
 #if MODULARIZE == 'instance'
+// In MODULARIZE=instance mode we delay most of the initialization work until
+// the `init` function is called.
 export default async function init(moduleArg = {}) {
   Module = moduleArg;
   processModuleArgs();
@@ -312,9 +314,21 @@ export default async function init(moduleArg = {}) {
   preInit();
   run();
 }
+
 #if PTHREADS
+// When run as a pthread we run `init` immediately.
 if (ENVIRONMENT_IS_PTHREAD) await init()
 #endif
+
+#if ENVIRONMENT_MAY_BE_NODE
+// When run as the main script under node we run `init` immediately.
+if (ENVIRONMENT_IS_NODE) {
+  const url = await import('url');
+  const isMainModule = url.pathToFileURL(process.argv[1]).href === import.meta.url;
+  if (isMainModule) await init();
+}
+#endif
+
 #else
 preInit();
 run();

test/common.py

@@ -1398,7 +1398,7 @@ def build(self, filename, libraries=None, includes=None, force_c=False, emcc_arg
     if emcc_args:
       all_emcc_args += emcc_args
     if not output_suffix:
-      if '-sEXPORT_ES6' in all_emcc_args or '-sWASM_ESM_INTEGRATION' in all_emcc_args:
+      if any(a in all_emcc_args for a in ('-sEXPORT_ES6', '-sWASM_ESM_INTEGRATION', '-sMODULARIZE=instance')):
         output_suffix = '.mjs'
       else:
         output_suffix = '.js'

test/test_core.py

@@ -6107,8 +6107,7 @@ def test_nl_types(self):
     self.do_core_test('test_nl_types.c')
 
   def test_799(self):
-    src = test_file('799.cpp')
-    self.do_runf(src, '''Set PORT family: 0, port: 3979
+    self.do_runf('799.cpp', '''Set PORT family: 0, port: 3979
 Get PORT family: 0
 PORT: 3979
 ''')
@@ -9596,6 +9595,9 @@ def test_esm_integration(self):
     self.assertContained('hello, world! (3)', self.run_js('runner.mjs'))
     self.assertFileContents(test_file('core/test_esm_integration.expected.mjs'), read_file('hello_world.mjs'))
 
+  def test_modularize_instance_hello(self):
+    self.do_core_test('test_hello_world.c', emcc_args=['-sMODULARIZE=instance', '-Wno-experimental'])
+
   @parameterized({
     '': ([],),
     'pthreads': (['-pthread'],),