docs: add --experimental-transform-types to docs

docs/api/command-line-switches.md

@@ -354,6 +354,11 @@ Affects the default output directory of [v8.setHeapSnapshotNearHeapLimit](https:
 
 Disable exposition of [Navigator API][] on the global scope from Node.js.
 
+### `--experimental-transform-types`
+
+Enables the [transformation](https://nodejs.org/api/typescript.html#type-stripping)
+of TypeScript-only syntax into JavaScript code.
+
 ## Chromium Flags
 
 There isn't a documented list of all Chromium switches, but there are a few ways to find them.

shell/common/node_bindings.cc

@@ -413,6 +413,7 @@ bool IsAllowedOption(const std::string_view option) {
           "--inspect-port",
           "--inspect-publish-uid",
           "--experimental-network-inspection",
+          "--experimental-transform-types",
       });
 
   // This should be aligned with what's possible to set via the process object.

spec/fixtures/type-stripping/basic.ts

@@ -0,0 +1,7 @@
+import { app } from 'electron/main';
+
+const logMessage = (message: string): void => console.log(message);
+
+logMessage('running');
+
+app.exit(0);

spec/fixtures/type-stripping/transform-types-node.ts

@@ -0,0 +1,9 @@
+enum Test {
+  A,
+  B,
+  C,
+}
+
+console.log(Test.A);
+
+process.exit(0);

spec/fixtures/type-stripping/transform-types.ts

@@ -0,0 +1,11 @@
+import { app } from 'electron/main';
+
+enum Test {
+  A,
+  B,
+  C,
+}
+
+console.log(Test.A);
+
+app.exit(0);

spec/node-spec.ts

@@ -1030,4 +1030,26 @@ describe('node feature', () => {
       });
     });
   });
+
+  describe('type stripping', () => {
+    it('strips TypeScript types automatically in the main process', async () => {
+      const child = childProcess.spawn(process.execPath, [path.join(fixtures, 'type-stripping', 'basic.ts')]);
+      const [code] = await once(child, 'exit');
+      expect(code).to.equal(0);
+    });
+
+    it('will not transform TypeScript types without --experimental-transform-types', async () => {
+      const child = childProcess.spawn(process.execPath, [path.join(fixtures, 'type-stripping', 'transform-types-node.ts')], {
+        env: { ELECTRON_RUN_AS_NODE: 'true' }
+      });
+      const [code] = await once(child, 'exit');
+      expect(code).to.not.equal(0);
+    });
+
+    it('transforms TypeScript types with --experimental-transform-types', async () => {
+      const child = childProcess.spawn(process.execPath, ['--experimental-transform-types', path.join(fixtures, 'type-stripping', 'transform-types.ts')]);
+      const [code] = await once(child, 'exit');
+      expect(code).to.equal(0);
+    });
+  });
 });