process: add process.features.typescript

Author: avivkeller

lib/internal/bootstrap/node.js

@@ -319,6 +319,21 @@ ObjectDefineProperty(process, 'features', {
 }
 
 const { emitWarning, emitWarningSync } = require('internal/process/warning');
+const { getOptionValue } = require('internal/options');
+
+let kTypeStrippingMode;
+ObjectDefineProperty(process.features, 'typescript', {
+  __proto__: null,
+  get() {
+    return kTypeStrippingMode ??= (
+      getOptionValue('--experimental-transform-types') ? 'transform' :
+        getOptionValue('--experimental-strip-types') ? 'strip' : ''
+    );
+  },
+  configurable: false,
+  enumerable: true,
+});
+
 process.emitWarning = emitWarning;
 internalBinding('process_methods').setEmitWarningSync(emitWarningSync);
 

test/es-module/test-typescript.mjs

@@ -313,3 +313,28 @@ test('execute a TypeScript file with CommonJS syntax requiring .mts with require
        match(result.stdout, /Hello, TypeScript!/);
        strictEqual(result.code, 0);
      });
+
+test('expect process.features.typescript to be \'strip\' when --experimental-strip-types', async () => {
+  const result = await spawnPromisified(process.execPath, [
+    '--experimental-strip-types',
+    '-p', 'process.features.typescript',
+  ]);
+
+  strictEqual(result.stdout, 'strip\n');
+  strictEqual(result.code, 0);
+  strictEqual(process.features.typescript, false);
+});
+
+test('expect process.features.typescript to be \'transform\' when --experimental-transform-types', async () => {
+  const result = await spawnPromisified(process.execPath, [
+    '--experimental-transform-types',
+    '-p', 'process.features.typescript',
+  ]);
+
+  strictEqual(result.stdout, 'transform\n');
+  strictEqual(result.code, 0);
+});
+
+test('expect process.features.typescript to be \'\' without type-stripping', async () => {
+  strictEqual(process.features.typescript, '');
+});

test/parallel/test-process-features.js

@@ -15,6 +15,7 @@ assert.deepStrictEqual(keys, new Set([
   'tls_ocsp',
   'tls',
   'cached_builtins',
+  'typescript',
 ]));
 
 for (const key of keys) {