fix: now working as a loader

README.md

@@ -21,10 +21,19 @@ Stack traces are preserved, by replacing removed types with white spaces.
 
 ```javascript
 const amaro = require('amaro');
-const { code } = amaro.transformSync("const foo: string = 'bar';");
+const { code } = amaro.transformSync("const foo: string = 'bar';", { mode: "strip-only" });
 console.log(code); // "const foo         = 'bar';"
 ```
 
+### Loader
+
+It is possible to use Amaro as an external loader to execute TypeScript files.
+This allows the installed Amaro to override the Amaro version used by Node.js.
+
+```bash
+node --experimental-strip-types --import="amaro/register" script.ts
+```
+
 ### How to update SWC
 
 To update the SWC version, run:

esbuild.config.js

@@ -0,0 +1,18 @@
+const { copy } = require("esbuild-plugin-copy");
+const esbuild = require("esbuild");
+
+esbuild.build({
+	entryPoints: ["src/index.ts"],
+	bundle: true,
+	platform: "node",
+	target: "node20",
+	outdir: "dist",
+	plugins: [
+		copy({
+			assets: {
+				from: ["./src/register/register.mjs"],
+				to: ["."],
+			},
+		}),
+	],
+});

package.json

@@ -21,7 +21,7 @@
 		"ci:fix": "biome check --write",
 		"prepack": "npm run build",
 		"postpack": "npm run clean",
-		"build": "esbuild --bundle --platform=node --target=node18 --outdir=dist src/index.ts",
+		"build": "node esbuild.config.js",
 		"typecheck": "tsc --noEmit",
 		"test": "node --test --experimental-test-snapshots \"**/*.test.js\"",
 		"test:regenerate": "node --test --experimental-test-snapshots --test-update-snapshots \"**/*.test.js\""
@@ -30,11 +30,13 @@
 		"@biomejs/biome": "1.8.3",
 		"@types/node": "^20.14.11",
 		"esbuild": "^0.23.0",
+		"esbuild-plugin-copy": "^2.1.1",
 		"rimraf": "^6.0.1",
 		"typescript": "^5.5.3"
 	},
-	"files": [
-		"dist",
-		"LICENSE.md"
-	]
+	"exports": {
+		".": "./dist/index.js",
+		"./register": "./dist/register.mjs"
+	},
+	"files": ["dist", "LICENSE.md"]
 }

src/loader.ts

@@ -1,14 +1,32 @@
-import swc from "../lib/wasm.js";
-import type { LoadHook } from "node:module";
-import { readFile } from "node:fs/promises";
+import assert from "node:assert";
+import type { LoadFnOutput, LoadHookContext } from "node:module";
+import { transformSync } from "./index.ts";
 
-export const load: LoadHook = async (source, context, nextLoad) => {
-	if (context.format?.includes("typescript")) {
-		const data = await readFile(source, "utf8");
+type NextLoad = (
+	url: string,
+	context?: LoadHookContext,
+) => LoadFnOutput | Promise<LoadFnOutput>;
+
+export async function load(
+	url: string,
+	context: LoadHookContext,
+	nextLoad: NextLoad,
+) {
+	const { format } = context;
+	if (format.endsWith("-typescript")) {
+		// Use format 'module' so it returns the source as-is, without stripping the types.
+		// Format 'commonjs' would not return the source for historical reasons.
+		const { source } = await nextLoad(url, {
+			...context,
+			format: "module",
+		});
+		if (source == null)
+			throw new Error("Source code cannot be null or undefined");
+		const { code } = transformSync(source.toString(), { mode: "strip-only" });
 		return {
-			source: swc.transformSync(data).code,
-			shortCircuit: true, // Skips bundled transpilation
+			format: format.replace("-typescript", ""),
+			source: code,
 		};
 	}
-	return { source: await nextLoad(source, context) };
-};
+	return nextLoad(url, context);
+}

src/register/register.mjs

@@ -0,0 +1,3 @@
+import { register } from "node:module";
+
+register("./index.js", import.meta.url);

src/transform.ts

@@ -7,7 +7,7 @@ const DEFAULT_OPTIONS: Options = {
 
 export function transformSync(
 	source: string,
-	options: Options,
+	options?: Options,
 ): TransformOutput {
 	// Ensure that the source code is a string
 	const input = `${source ?? ""}`;

test/fixtures/enum.ts

@@ -1,4 +1,4 @@
 enum Foo {
-    A = "Hello, TypeScript!"
+	A = "Hello, TypeScript!",
 }
 console.log(Foo.A);

test/loader.test.js

@@ -6,7 +6,7 @@ test("should work as a loader", async () => {
 	const result = await spawnPromisified(process.execPath, [
 		"--experimental-strip-types",
 		"--no-warnings",
-		"--import=./dist/index.js",
+		"--import=./dist/register.mjs",
 		fixturesPath("hello.ts"),
 	]);
 
@@ -19,11 +19,11 @@ test("should work with enums", async () => {
 	const result = await spawnPromisified(process.execPath, [
 		"--experimental-strip-types",
 		"--no-warnings",
-		"--import=./dist/index.js",
+		"--import=./dist/register.mjs",
 		fixturesPath("enum.ts"),
 	]);
 
-	strictEqual(result.stderr, "");
-	match(result.stdout, /Hello, TypeScript!/);
-	strictEqual(result.code, 0);
+	strictEqual(result.stdout, "");
+	match(result.stderr, /TypeScript enum is not supported in strip-only mode/);
+	strictEqual(result.code, 1);
 });