Node erases a type assertion, so `typeof (stored as R).member` reads the property off whichever value is stored: when `stored` is `R | Record<K, R>` and the record arm is holding, the read answers undefined and the probe is false. Two earlier decisions made this throw instead. lowerAsExpression applied the checked union extraction for `stored as R` eagerly, trapping on exactly the arm the probe exists to detect; and lowerFieldRead answered the read from the ASSERTED checker type, which also folded `typeof` to a constant. Defer the assertion's extraction for a member PRESENCE PROBE - the operand of `typeof`, or an operand of `===`/`!==`/`==`/`!=` against undefined, null or `void 0` - when the stored union's record arms declare the member unevenly. The read then answers per arm off the runtime tag (assertedMemberRead), each declaring arm reading its slot and the rest answering undefined; a read with no per-arm answer still applies the extraction the assertion would have taken. `"member" in (stored as R)` over the same shape likewise probes the stored value. Every real use - the member called, compared by identity, read into a typed slot - keeps the checked extraction, so a lying assertion still throws at its use. Types don't lie; a probe simply isn't the use. Corpus program asserted-arm-probe.ts covers typeof, undefined and nullish probes on the optional and required shapes, `in` on the required shape, a probe guarding the real call, and a real use that throws. 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.