module: fix extensionless typescript in cjs loader

lib/internal/modules/cjs/loader.js

@@ -653,9 +653,13 @@ function getDefaultExtensions() {
   let extensions = ObjectKeys(Module._extensions);
   const tsEnabled = getOptionValue('--experimental-strip-types');
   if (tsEnabled) {
+    // remove .ts and .cts from the default extensions
+    // to avoid extensionless require of .ts and .cts files.
+    // it behaves similarly to how .mjs is handled when --experimental-require-module
+    // is enabled.
     extensions = ArrayPrototypeFilter(extensions, (ext) =>
-      ext !== '.ts' || Module._extensions['.ts'] !== loadTS ||
-      ext !== '.cts' || Module._extensions['.ts'] !== loadCTS,
+      (ext !== '.ts' || Module._extensions['.ts'] !== loadTS) &&
+      (ext !== '.cts' || Module._extensions['.cts'] !== loadCTS),
     );
   }
 

test/es-module/test-typescript-commonjs.mjs

@@ -18,8 +18,6 @@ test('require a .ts file with explicit extension succeeds', async () => {
   strictEqual(result.code, 0);
 });
 
-// TODO(marco-ippolito) This test should fail because extensionless require
-// but it's behaving like a .js file
 test('eval require a .ts file with implicit extension fails', async () => {
   const result = await spawnPromisified(process.execPath, [
     '--experimental-strip-types',
@@ -30,23 +28,36 @@ test('eval require a .ts file with implicit extension fails', async () => {
     cwd: fixtures.path('typescript/ts'),
   });
 
-  strictEqual(result.stderr, '');
-  match(result.stdout, /Hello, TypeScript!/);
-  strictEqual(result.code, 0);
+  strictEqual(result.stdout, '');
+  match(result.stderr, /Error: Cannot find module/);
+  strictEqual(result.code, 1);
+});
+
+test('eval require a .cts file with implicit extension fails', async () => {
+  const result = await spawnPromisified(process.execPath, [
+    '--experimental-strip-types',
+    '--eval',
+    'require("./test-cts-typescript")',
+    '--no-warnings',
+  ], {
+    cwd: fixtures.path('typescript/ts'),
+  });
+
+  strictEqual(result.stdout, '');
+  match(result.stderr, /Error: Cannot find module/);
+  strictEqual(result.code, 1);
 });
 
-// TODO(marco-ippolito) This test should fail because extensionless require
-// but it's behaving like a .js file
 test('require a .ts file with implicit extension fails', async () => {
   const result = await spawnPromisified(process.execPath, [
     '--experimental-strip-types',
     '--no-warnings',
     fixtures.path('typescript/cts/test-extensionless-require.ts'),
   ]);
 
-  strictEqual(result.stderr, '');
-  match(result.stdout, /Hello, TypeScript!/);
-  strictEqual(result.code, 0);
+  strictEqual(result.stdout, '');
+  match(result.stderr, /Error: Cannot find module/);
+  strictEqual(result.code, 1);
 });
 
 test('expect failure of an .mts file with CommonJS syntax', async () => {

test/fixtures/typescript/ts/test-cts-typescript.cts

@@ -0,0 +1,5 @@
+const str: string = "Hello, TypeScript!";
+interface Foo {
+    bar: string;
+}
+console.log(str);