check without extensions

lib/internal/modules/esm/resolve.js

@@ -246,8 +246,26 @@ function finalizeResolution(resolved, base, preserveSymlinks) {
     throw err;
   }
 
-  const stats = internalFsBinding.internalModuleStat(toNamespacedPath(StringPrototypeEndsWith(path, '/') ?
-    StringPrototypeSlice(path, -1) : path));
+  let stats;
+  path = StringPrototypeEndsWith(path, '/') ? StringPrototypeSlice(path, 0, -1) : path;
+  if (getOptionValue('--experimental-typescript')) {
+
+    stats = internalFsBinding.internalModuleStat(toNamespacedPath(path));
+    switch (stats) {
+      case 0:
+        // Found the file
+        break;
+      case 1:
+        throw new ERR_UNSUPPORTED_DIR_IMPORT(path, fileURLToPath(base), String(resolved));
+      default:
+        // Try with .ts extension
+        path += '.ts';
+        stats = internalFsBinding.internalModuleStat(path);
+        break;
+    }
+  } else {
+    stats = internalFsBinding.internalModuleStat(path);
+  }
 
   // Check for stats.isDirectory()
   if (stats === 1) {

test/fixtures/typescript/test-import-no-extension.ts

@@ -0,0 +1,2 @@
+import { a } from './a';
+console.log(a);

test/parallel/test-typescript.js

@@ -45,3 +45,17 @@ test('execute a typescript with node_modules', async () => {
     stdout: 'Hello, TypeScript!\n',
   });
 });
+
+test('execute a typescript file with imports with no extensions', async () => {
+  const result = await spawnPromisified(process.execPath, [
+    '--experimental-typescript',
+    fixtures.path('typescript/test-import-no-extension.ts'),
+  ]);
+
+  deepStrictEqual(result, {
+    code: 0,
+    signal: null,
+    stderr: '',
+    stdout: 'Hello, TypeScript!\n',
+  });
+});