Malte UblandClaude Opus 5.5 15cc7310ac Keep record values that subtype reduction folds into an inferred type
TypeScript infers a function's return type as the subtype-reduced union of
the values it returns: returning `{ status }` in one branch and
`{ status, value }` (or a call returning either) in another infers just
`{ status }`. Records have fixed layouts, so that type cannot hold the
second value: the return failed its union wrap at run time ('... is not
representable in the target union'), and values that reached a binding of
the reduced type failed a checked narrowing.

- A function with an inferred return type and no contextual signature
  returns the union of the record types it actually returns, including
  through calls of other such functions. Only value types the checker's
  reduction dropped from the inferred union are added, so functions whose
  inferred type already names every returned type keep their layout.
  Declared return types keep their meaning.
- Reading such a union through the reduced type (a binding, a member read,
  JSON.stringify) uses a dedicated checked extraction that converts the wider
  record arms with the ordinary width coercion; other narrowings are
  unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-23 18:26:39 -07:00
2026-10-16 10:33:14 -05:00
2026-10-14 17:27:02 -05:00
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2026-07-22 18:08:04 -05:00

scriptc

Vercel Labs Experiment npm version: scriptc License: Apache-2.0 npm downloads per month: scriptc

scriptc compiles TypeScript and JavaScript to native executables and WebAssembly. It uses the types checked by the TypeScript compiler to generate machine code, and the output runs without Node.js installed. npm packages your program imports compile along with it. Code scriptc can't compile is reported at build time with a diagnostic and, where available, a rewrite hint.

scriptc is experimental and supports a subset of JavaScript, TypeScript, and Node.js APIs. Run scriptc coverage on an existing program to see how much of it compiles, and see the limitations and Node.js compatibility reference for details.

Installation

Install with Node.js 24 or later and npm:

$ npm install -g scriptc

The installed compiler runs natively on macOS, Linux, and Windows. Node.js is needed only to install it and to run WASI modules with scriptc run. Standalone compiler archives are also available from GitHub Releases.

Building executables requires a linker and the platform SDK or sysroot. See the quickstart for prerequisites and platform support for host requirements, cross-compilation, and WebAssembly.

Build a program

Create hello.ts:

const who = process.argv.length > 2 ? process.argv[2] : "world";
console.log(`hello, ${who}`);

scriptc run compiles the file and runs the result:

$ scriptc run hello.ts
hello, world

scriptc build writes an executable:

$ scriptc build hello.ts -o hello >/dev/null
$ ./hello scriptc
hello, scriptc

These examples use POSIX shell syntax. On Windows, build hello.exe and run it with .\hello.exe.

Use scriptc coverage hello.ts to check what compiles before you build. See coverage reports for details.

Use Node APIs

Supported Node APIs compile to the native runtime. For example, server.ts:

import { createServer } from "node:http";

const server = createServer((req, res) => {
  res.setHeader("content-type", "application/json");
  res.end(JSON.stringify({ path: req.url }));
});

server.listen(8080, () => {
  console.log("listening on http://localhost:8080");
});
$ scriptc build server.ts -o server >/dev/null
$ ./server
listening on http://localhost:8080

Use npm packages

npm packages compile into the executable with your code, so it doesn't read node_modules at runtime.

Create cli.ts:

import pc from "picocolors";

console.log(pc.green("hello from scriptc"));
$ npm install picocolors
$ scriptc build cli.ts -o cli >/dev/null
$ ./cli
hello from scriptc

Package support is partial. See npm dependencies for which packages compile and how to check them.

Documentation

Contributing

See CONTRIBUTING.md for source setup, testing, native artifact builds, and docs development.

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