From c9174a26e4f348d200d692879aea5ceb0337d9b8 Mon Sep 17 00:00:00 2001
From: avivkeller <me@aviv.sh>
Date: Mon, 22 Jun 2026 20:42:18 -0400
Subject: [PATCH] repl: add experimental TypeScript support

Adds experimental TypeScript support to
the REPL, opt-in-able via the
`--experimental-repl-typescript` flag.

Signed-off-by: avivkeller <me@aviv.sh>
---
 doc/api/cli.md                        | 10 ++++++++++
 lib/internal/modules/typescript.js    |  1 +
 lib/repl.js                           | 19 +++++++++++++++++--
 src/node_options.cc                   |  4 ++++
 src/node_options.h                    |  1 +
 test/parallel/test-repl-typescript.js | 23 +++++++++++++++++++++++
 6 files changed, 56 insertions(+), 2 deletions(-)
 create mode 100644 test/parallel/test-repl-typescript.js

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 79f02ee5eddd86..c2d81e2ff0a6eb 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -1362,6 +1362,16 @@ added:
 
 Enable experimental support for the QUIC protocol.
 
+### `--experimental-repl-typescript`
+
+<!--
+added: REPLACEME
+-->
+
+> Stability: 1.2 - Release candidate
+
+Enable experimental support for TypeScript stripping in the REPL.
+
 ### `--experimental-sea-config`
 
 <!-- YAML
diff --git a/lib/internal/modules/typescript.js b/lib/internal/modules/typescript.js
index 43bc57d977ec27..2a777af490bcf0 100644
--- a/lib/internal/modules/typescript.js
+++ b/lib/internal/modules/typescript.js
@@ -185,4 +185,5 @@ module.exports = {
   stripTypeScriptModuleTypes,
   stripTypeScriptTypes,
   stripTypeScriptTypesForCoverage,
+  processTypeScriptCode,
 };
diff --git a/lib/repl.js b/lib/repl.js
index 17aab1c409beca..2130487b13d845 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -95,12 +95,14 @@ const {
 const acornWalk = require('internal/deps/acorn/acorn-walk/dist/walk');
 const {
   decorateErrorStack,
+  emitExperimentalWarning,
   isError,
   deprecate,
   SideEffectFreeRegExpPrototypeSymbolReplace,
   SideEffectFreeRegExpPrototypeSymbolSplit,
 } = require('internal/util');
 const { inspect } = require('internal/util/inspect');
+const { processTypeScriptCode } = require('internal/modules/typescript');
 const vm = require('vm');
 
 const { runInThisContext, runInContext } = vm.Script.prototype;
@@ -141,6 +143,10 @@ const {
 const experimentalREPLAwait = getOptionValue(
   '--experimental-repl-await',
 );
+const experimentalREPLTypeScript = getOptionValue(
+  '--experimental-repl-typescript',
+);
+
 const pendingDeprecation = getOptionValue('--pending-deprecation');
 const {
   REPL_MODE_SLOPPY,
@@ -241,6 +247,11 @@ function removeProcessNewListener() {
 
 fixReplRequire(module);
 
+const tsOptions = { __proto__: null, mode: 'transform' };
+if (experimentalREPLTypeScript) {
+  emitExperimentalWarning('TypeScript support in the REPL');
+}
+
 // This is the default "writer" value, if none is passed in the REPL options,
 // and it can be overridden by custom print functions, such as `probe` or
 // `eyes.js`.
@@ -499,7 +510,9 @@ class REPLServer extends Interface {
             const fallbackCode = SideEffectFreeRegExpPrototypeSymbolReplace(/\bawait\b/g, code, '');
             try {
               makeContextifyScript(
-                fallbackCode,            // code
+                experimentalREPLTypeScript ?
+                  processTypeScriptCode(fallbackCode, tsOptions) :
+                  fallbackCode, // code
                 file,                    // filename,
                 0,                       // lineOffset
                 0,                       // columnOffset,
@@ -537,7 +550,9 @@ class REPLServer extends Interface {
               code = `'use strict'; void 0;\n${code}`;
             }
             script = makeContextifyScript(
-              code,                    // code
+              experimentalREPLTypeScript ?
+                processTypeScriptCode(code, tsOptions) :
+                code, // code
               file,                    // filename,
               0,                       // lineOffset
               0,                       // columnOffset,
diff --git a/src/node_options.cc b/src/node_options.cc
index b7eadef850f75d..717820a8a1dcf8 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -726,6 +726,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             &EnvironmentOptions::experimental_repl_await,
             kAllowedInEnvvar,
             true);
+  AddOption("--experimental-repl-typescript",
+            "experimental TypeScript support in REPL",
+            &EnvironmentOptions::experimental_repl_typescript,
+            kAllowedInEnvvar);
   AddOption("--experimental-vm-modules",
             "experimental ES Module support in vm module",
             &EnvironmentOptions::experimental_vm_modules,
diff --git a/src/node_options.h b/src/node_options.h
index f7a8a999d85a1b..077177f7159b8f 100644
--- a/src/node_options.h
+++ b/src/node_options.h
@@ -154,6 +154,7 @@ class EnvironmentOptions : public Options {
   bool allow_ffi = false;
   bool allow_worker_threads = false;
   bool experimental_repl_await = true;
+  bool experimental_repl_typescript = false;
   bool experimental_vm_modules = EXPERIMENTALS_DEFAULT_VALUE;
   bool async_context_frame = true;
   bool expose_internals = false;
diff --git a/test/parallel/test-repl-typescript.js b/test/parallel/test-repl-typescript.js
new file mode 100644
index 00000000000000..faba7af8f2a7e9
--- /dev/null
+++ b/test/parallel/test-repl-typescript.js
@@ -0,0 +1,23 @@
+// Flags: --experimental-repl-typescript
+'use strict';
+require('../common');
+const assert = require('assert');
+
+const { startNewREPLServer } = require('../common/repl');
+
+const { input, output } = startNewREPLServer({ terminal: false, prompt: '> ' });
+
+input.emit('data', 'let x: number = 3\n');
+assert.match(output.accumulator, /undefined\n> /);
+output.accumulator = '';
+
+input.emit('data', 'x\n');
+assert.match(output.accumulator, /3\n> /);
+
+// Transform TypeScript to JavaScript and evaluate it
+input.emit('data', 'enum Color { Red, Green, Blue }\n');
+assert.match(output.accumulator, /undefined\n> /);
+output.accumulator = '';
+
+input.emit('data', 'Color.Reed\n');
+assert.match(output.accumulator, /0\n> /);