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repl: add experimental TypeScript support #64077

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0badde7
repl: add experimental TypeScript support
avivkeller Jun 23, 2026
1975c6e
fixup!
avivkeller Jun 23, 2026
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10 changes: 10 additions & 0 deletions doc/api/cli.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1362,6 +1362,16 @@ added:
Enable experimental support for the QUIC protocol.

### `--experimental-repl-typescript`

<!--
added: REPLACEME
-->

> Stability: 1.2 - Release candidate

@marco-ippolito marco-ippolito Jun 23, 2026

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Why release candidate

@avivkeller avivkeller Jun 23, 2026

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The underlying transformer, https://nodejs.org/api/module.html#modulestriptypescripttypescode-options, is a release candidate, I figured this would be an extension of that

@marco-ippolito marco-ippolito Jun 23, 2026

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I think this has a larger scope than that api

Enable experimental support for TypeScript stripping in the REPL.

### `--experimental-sea-config`

<!-- YAML
Expand Down
6 changes: 5 additions & 1 deletion lib/internal/main/check_syntax.js
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ function loadESMIfNeeded(cb) {

async function checkSyntax(source, filename) {
let format;
if (filename === '[stdin]' || filename === '[eval]') {
if (filename === '[stdin]' || filename === '[eval]' || filename === '[repl]') {
format = (getOptionValue('--input-type') === 'module') ? 'module' : 'commonjs';
} else {
const { defaultResolve } = require('internal/modules/esm/resolve');
Expand All @@ -75,3 +75,7 @@ async function checkSyntax(source, filename) {

wrapSafe(filename, source, undefined, format);
}

module.exports = {
checkSyntax,
};
1 change: 1 addition & 0 deletions lib/internal/modules/typescript.js
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Expand Up @@ -185,4 +185,5 @@ module.exports = {
stripTypeScriptModuleTypes,
stripTypeScriptTypes,
stripTypeScriptTypesForCoverage,
processTypeScriptCode,
};
68 changes: 46 additions & 22 deletions lib/repl.js
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Expand Up @@ -97,6 +97,7 @@ const {
decorateErrorStack,
isError,
deprecate,
getLazy,
SideEffectFreeRegExpPrototypeSymbolReplace,
SideEffectFreeRegExpPrototypeSymbolSplit,
} = require('internal/util');
Expand Down Expand Up @@ -141,6 +142,9 @@ const {
const experimentalREPLAwait = getOptionValue(
'--experimental-repl-await',
);
const experimentalREPLTypeScript = getOptionValue(
'--experimental-repl-typescript',
);
const pendingDeprecation = getOptionValue('--pending-deprecation');
const {
REPL_MODE_SLOPPY,
Expand Down Expand Up @@ -177,8 +181,12 @@ const {

// Lazy-loaded.
let processTopLevelAwait;
const processTypeScriptCode = getLazy(() => require('internal/modules/typescript').processTypeScriptCode);
const checkSyntax = getLazy(() => require('internal/main/check_syntax').checkSyntax);

const parentModule = module;
const kREPLTag = '[repl]';
const kTypeScriptOptions = { __proto__: null, mode: 'strip-only', filename: kREPLTag };

// AsyncLocalStorage to track which REPL instance owns the current async context
// This replaces the domain-based tracking for error handling
Expand Down Expand Up @@ -477,6 +485,42 @@ class REPLServer extends Interface {
phase === 'evaluation' ? cascadedLoader.kEvaluationPhase :
cascadedLoader.kSourcePhase);
}

function runScript(scriptCode) {
if (experimentalREPLTypeScript) {
try {
// Try parsing as pure JS
checkSyntax()(scriptCode, kREPLTag);
} catch (originalError) {
try {
// That failed, so try stripping TypeScript types
scriptCode = processTypeScriptCode()(scriptCode, kTypeScriptOptions);
} catch (tsError) {
// If it's invalid or unsupported TypeScript syntax, rethrow the original error
// with the TypeScript error message added to the stack.
if (tsError.code === 'ERR_INVALID_TYPESCRIPT_SYNTAX' ||
tsError.code === 'ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX') {
originalError.stack = `${tsError.message}\n\n${originalError.stack}`;
throw originalError;
}

throw tsError;
}
}
}

return makeContextifyScript(
scriptCode, // code
file, // filename,
0, // lineOffset
0, // columnOffset,
undefined, // cachedData
false, // produceCachedData
undefined, // parsingContext
hostDefinedOptionId, // hostDefinedOptionId
importModuleDynamically, // importModuleDynamically
);
}
// `experimentalREPLAwait` is set to true by default.
// Shall be false in case `--no-experimental-repl-await` flag is used.
if (experimentalREPLAwait && StringPrototypeIncludes(code, 'await')) {
Expand All @@ -498,17 +542,7 @@ class REPLServer extends Interface {
// in order to detect if error is truly non recoverable
const fallbackCode = SideEffectFreeRegExpPrototypeSymbolReplace(/\bawait\b/g, code, '');
try {
makeContextifyScript(
fallbackCode, // code
file, // filename,
0, // lineOffset
0, // columnOffset,
undefined, // cachedData
false, // produceCachedData
undefined, // parsingContext
hostDefinedOptionId, // hostDefinedOptionId
importModuleDynamically, // importModuleDynamically
);
runScript(fallbackCode);
} catch (fallbackError) {
if (isRecoverableError(fallbackError, fallbackCode)) {
recoverableError = true;
Expand Down Expand Up @@ -536,17 +570,7 @@ class REPLServer extends Interface {
// value for statements and declarations that don't return a value.
code = `'use strict'; void 0;\n${code}`;
}
script = makeContextifyScript(
code, // code
file, // filename,
0, // lineOffset
0, // columnOffset,
undefined, // cachedData
false, // produceCachedData
undefined, // parsingContext
hostDefinedOptionId, // hostDefinedOptionId
importModuleDynamically, // importModuleDynamically
);
script = runScript(code);
} catch (e) {
debug('parse error %j', code, e);
if (wrappedCmd) {
Expand Down
4 changes: 4 additions & 0 deletions src/node_options.cc
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Expand Up @@ -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,
Expand Down
1 change: 1 addition & 0 deletions src/node_options.h
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Expand Up @@ -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;

@marco-ippolito marco-ippolito Jun 23, 2026

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Suggested change
bool experimental_repl_typescript = false;
bool experimental_repl_typescript = EXPERIMENTALS_DEFAULT_VALUE;

bool experimental_vm_modules = EXPERIMENTALS_DEFAULT_VALUE;
bool async_context_frame = true;
bool expose_internals = false;
Expand Down
15 changes: 15 additions & 0 deletions test/parallel/test-repl-typescript.js
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@@ -0,0 +1,15 @@
// 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> /);

Check failure on line 11 in test/parallel/test-repl-typescript.js

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GitHub Actions / aarch64-darwin: with shared libraries 

--- stderr ---
node:internal/assert/utils:146
  throw error;
  ^

AssertionError [ERR_ASSERTION]: The input did not match the regular expression /undefined\n> /. Input:

'> Uncaught Error [ERR_NO_TYPESCRIPT]: Node.js is not compiled with TypeScript support\n' +
  '    at assertTypeScript (node:internal/util:247:11)\n' +
  '    at node:internal/modules/typescript:35:3 {\n' +
  "  code: 'ERR_NO_TYPESCRIPT'\n" +
  '}\n' +
  '> '

    at Object.<anonymous> (/Users/runner/work/_temp/node-v27.0.0-nightly2026-06-23c03c9f82e8-slim/test/parallel/test-repl-typescript.js:11:8)
    at Module._compile (node:internal/modules/cjs/loader:1947:14)
    at Object..js (node:internal/modules/cjs/loader:2087:10)
    at Module.load (node:internal/modules/cjs/loader:1669:32)
    at Module._load (node:internal/modules/cjs/loader:1450:12)
    at wrapModuleLoad (node:internal/modules/cjs/loader:260:19)
    at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:154:5)
    at node:internal/main/run_main_module:33:47 {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: '> Uncaught Error [ERR_NO_TYPESCRIPT]: Node.js is not compiled with TypeScript support\n' +
    '    at assertTypeScript (node:internal/util:247:11)\n' +
    '    at node:internal/modules/typescript:35:3 {\n' +
    "  code: 'ERR_NO_TYPESCRIPT'\n" +
    '}\n' +
    '> ',
  expected: /undefined\n> /,
  operator: 'match',
  diff: 'simple'
}

Node.js v27.0.0-pre
Command: out/Release/node --experimental-repl-typescript /Users/runner/work/_temp/node-v27.0.0-nightly2026-06-23c03c9f82e8-slim/test/parallel/test-repl-typescript.js

Check failure on line 11 in test/parallel/test-repl-typescript.js

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GitHub Actions / x86_64-darwin: with shared libraries 

--- stderr ---
node:internal/assert/utils:146
  throw error;
  ^

AssertionError [ERR_ASSERTION]: The input did not match the regular expression /undefined\n> /. Input:

'> Uncaught Error [ERR_NO_TYPESCRIPT]: Node.js is not compiled with TypeScript support\n' +
  '    at assertTypeScript (node:internal/util:247:11)\n' +
  '    at node:internal/modules/typescript:35:3 {\n' +
  "  code: 'ERR_NO_TYPESCRIPT'\n" +
  '}\n' +
  '> '

    at Object.<anonymous> (/Users/runner/work/_temp/node-v27.0.0-nightly2026-06-23c03c9f82e8-slim/test/parallel/test-repl-typescript.js:11:8)
    at Module._compile (node:internal/modules/cjs/loader:1947:14)
    at Object..js (node:internal/modules/cjs/loader:2087:10)
    at Module.load (node:internal/modules/cjs/loader:1669:32)
    at Module._load (node:internal/modules/cjs/loader:1450:12)
    at wrapModuleLoad (node:internal/modules/cjs/loader:260:19)
    at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:154:5)
    at node:internal/main/run_main_module:33:47 {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: '> Uncaught Error [ERR_NO_TYPESCRIPT]: Node.js is not compiled with TypeScript support\n' +
    '    at assertTypeScript (node:internal/util:247:11)\n' +
    '    at node:internal/modules/typescript:35:3 {\n' +
    "  code: 'ERR_NO_TYPESCRIPT'\n" +
    '}\n' +
    '> ',
  expected: /undefined\n> /,
  operator: 'match',
  diff: 'simple'
}

Node.js v27.0.0-pre
Command: out/Release/node --experimental-repl-typescript /Users/runner/work/_temp/node-v27.0.0-nightly2026-06-23c03c9f82e8-slim/test/parallel/test-repl-typescript.js
output.accumulator = '';

input.emit('data', 'x\n');
assert.match(output.accumulator, /3\n> /);
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