A record built from the checked-dynamic tree keeps the own keys its shape
does not declare, and every JS copy carries them. `%rec.capture` (the
closed-to-index-signature width reshape) rebuilt the target from the
source's DECLARED fields only, so those keys vanished with no diagnostic.
The shape that made this visible is an inline, unannotated async arrow in
a generic call:
interface T { transformHeaders?(h: H): H | Promise<H> }
async function f<O extends T>(o: O | undefined) { … }
f({ transformHeaders: async (h) => ({ ...h, x: "1" }) })
No contextual type reaches the arrow through the type parameter, so its
return slot is contextualized by tsc's own inference, which drops the
spread's index signature: the closure is typed Promise<{ x }> and its body
lowers through the checked-dynamic spread into that closed record — the
keys survive in the record's kept source view. The call site reads the
member through the declared H and adapts the function value, and that
ovf capture dropped `accept`. Node prints "accept,x".
When the source kept such a view, rebuild the target from that live view
instead of the static field list: the same validated keyed conversion the
checked record builder performs, which copies exactly the keys Node
copies. Everything else keeps the existing field-by-field copy.
A program whose functions never convert a checked-dynamic value into a
closed record cannot keep such a view anywhere, so the capture asks the
program too: one lazy scan over every lowered function settles whether a
kept source is possible at all, and only then does the helper finalize its
body with the branch. The scan looks through union arms, promise values,
and array elements; a union reached while it is already being visited
contributes nothing until the outer union settles, and an answer that
depended on such a cycle is not memoized, because another entry into the
cycle may reach the arm it could not see. Programs without such a
conversion keep the previous helper byte for byte and link no
checked-dynamic conversion code.
tests/corpus/record-source-keys-index-capture.ts pins the drop both ways:
the inline block-bodied async arrow (assigned through the await and read
into a local first) and the async method form print the caller keys on the
base compiler and match Node byte for byte with this change, while the
non-generic, expression-bodied, nested-field and sync-arrow forms are
controls that already matched on both.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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
- Introduction: what scriptc is and what you can build.
- Quickstart: installation and your first executable.
- Coverage reports: check whether an existing program compiles.
- Platform support: cross-compilation and WebAssembly.
- CLI reference: commands, options, and output formats.
- Native program objects: use compiler output in external builds.
- Native FFI: call C ABI functions from compiled programs.
- WebAssembly modules: build and embed WASI modules.
- Examples: programs and integration examples in this repository.
Contributing
See CONTRIBUTING.md for source setup, testing, native artifact builds, and docs development.