[GroophyLifefor]

swc only reads options.transform in "transform" mode, but transformSync sends it on every call and swc deserializes it each time. In "strip-only" mode (the default, used by Node.js) this change leaves it out. "transform" mode and caller-provided options are unchanged.

JS ↔ wasm calls per transformSync call: 389 -> 214. Output is identical (all TypeScript fixtures in Node.js test/fixtures, including error cases). npm test passes.

Benchmark

Node.js benchmark/ts/strip-typescript.js with compare.js, 30 runs per binary. Same Node.js build before and after; only the bundled amaro differs.

amaro in Node.js	Fixture	Before	After	Improvement	95% confidence interval
main (1.2.1)	.ts	5,175 imports/s (193.2 µs)	5,542 imports/s (180.5 µs)	+7.07%	+5.64% … +8.51%
main (1.2.1)	.js (control)	13,061 imports/s	13,037 imports/s	−0.19%	−1.45% … +1.07% (no change)
1.1.11 (bundled today)	.ts	5,094 imports/s (196.3 µs)	5,539 imports/s (180.5 µs)	+8.74%	+6.87% … +10.61%
1.1.11 (bundled today)	.js (control)	13,121 imports/s	13,098 imports/s	−0.17%	−1.35% … +1.00% (no change)

Environment

• CPU: AMD Ryzen AI 7 350 (8 cores / 16 threads), benchmark pinned to one core with taskset -c 0
• RAM: 24 Gb
• OS: Ubuntu 26.04.1 LTS, Linux 7.0.0-38-generic, power profile balanced, governor powersave
• Node.js: main at 269cab6320 (v27.0.0-pre), built with ninja
• amaro main: dist/index.js and dist/internal.js bundled into one file with esbuild so Node.js can embed it, the same way before and after

[marco-ippolito]

it makes sense but I think we can refactor the whole function in a cleaner way, give there are only 2 possible options

[GroophyLifefor]

Hey @marco-ippolito, What's the idea you have in mind? I can work on it.

[marco-ippolito]

In the object signature we could default options to type stripping default options. Then in the body if mode is transform, merge default transform object with options.

[GroophyLifefor]

Is it something like this?

const DEFAULT_OPTIONS = {
	mode: "strip-only",
	deprecatedTsModuleAsError: true,
} as Options;

const DEFAULT_TRANSFORM_OPTIONS = {
	verbatimModuleSyntax: true,
	nativeClassProperties: true,
	noEmptyExport: true,
	importNotUsedAsValues: "preserve",
} as Options["transform"];

export function transformSync(
	source: string,
	options: Options = DEFAULT_OPTIONS,
): TransformOutput {
	const input = `${source ?? ""}`;
	const opts = { ...DEFAULT_OPTIONS, ...options };
	if (opts.mode === "transform") {
		opts.transform = { ...DEFAULT_TRANSFORM_OPTIONS, ...opts.transform };
	}
	return swc.transformSync(input, opts);
}

Two things to check:

• transformSync(src, { filename }) (what Node.js does) doesn't use the default parameter, so deprecatedTsModuleAsError: true would be lost. That's why I still merge with DEFAULT_OPTIONS inside.
• With { mode: "transform", transform: { noEmptyExport: false } }, today only { noEmptyExport: false } is sent. With this code the other three defaults are filled in. Is that change OK, or should a user's transform keep replacing the defaults like today?

[marco-ippolito]

I was thinking something simple like:

const DEFAULT_OPTIONS = {
	mode: "strip-only",
	deprecatedTsModuleAsError: true,
} satisfies Options;

// swc only reads `transform` in "transform" mode, so these defaults are kept
// out of strip-only calls to avoid deserializing them on every call.
const DEFAULT_TRANSFORM_OPTIONS = {
	mode: "transform",
	deprecatedTsModuleAsError: true,
	transform: {
		verbatimModuleSyntax: true,
		nativeClassProperties: true,
		noEmptyExport: true,
		importNotUsedAsValues: "preserve",
	},
} satisfies Options;

export function transformSync(
	source: string,
	options?: Options,
): TransformOutput {
	// Ensure that the source code is a string
	const input = `${source ?? ""}`;
	const defaults =
		options?.mode === "transform" ? DEFAULT_TRANSFORM_OPTIONS : DEFAULT_OPTIONS;
	return swc.transformSync(input, { ...defaults, ...options });
}

[GroophyLifefor]

Pretty clear, let me implement in this PR.