fix: use detected format

src/strip-loader.ts

@@ -13,12 +13,10 @@ export async function load(
 ) {
 	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.
 		try {
 			const { source } = await nextLoad(url, {
 				...context,
-				format: "module",
+				format,
 			});
 			// biome-ignore lint/style/noNonNullAssertion: If module exists, it will have a source
 			const { code } = transformSync(source!.toString(), {

src/transform-loader.ts

@@ -15,11 +15,9 @@ export async function load(
 	const { format } = context;
 	if (format?.endsWith("-typescript")) {
 		try {
-			// 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",
+				format,
 			});
 
 			// biome-ignore lint/style/noNonNullAssertion: If module exists, it will have a source

test/fixtures/commonjs.cts

@@ -0,0 +1,9 @@
+const message: string = "Hello from CommonJS TypeScript (.cts)!";
+
+function greet(name: string): void {
+    console.log(`${message} - ${name}`);
+}
+
+module.exports = { greet };
+
+greet("Test");

test/fixtures/commonjs.ts

@@ -0,0 +1,9 @@
+const message: string = "Hello from CommonJS TypeScript!";
+
+function greet(name: string): void {
+    console.log(`${message} - ${name}`);
+}
+
+module.exports = { greet };
+
+greet("Test");

test/fixtures/esm.mts

@@ -0,0 +1,7 @@
+const message: string = "Hello from ESM TypeScript!";
+
+export function greet(name: string): void {
+    console.log(`${message} - ${name}`);
+}
+
+greet("Test");

test/fixtures/esm/esm.ts

@@ -0,0 +1,7 @@
+const message: string = "Hello from ESM TypeScript!";
+
+export function greet(name: string): void {
+    console.log(`${message} - ${name}`);
+}
+
+greet("Test");

test/fixtures/esm/package.json

@@ -0,0 +1 @@
+{}

test/loader.test.js

@@ -99,3 +99,99 @@ test("should throw syntax error for invalid typescript", async (t) => {
 	match(result.stderr, /await isn't allowed in non-async function/);
 	strictEqual(result.code, 1);
 });
+
+test("should work with commonjs typescript files using strip", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-strip.mjs",
+		fixturesPath("commonjs.ts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from CommonJS TypeScript!/);
+	strictEqual(result.code, 0);
+});
+
+test("should work with commonjs typescript files using transform", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-transform.mjs",
+		fixturesPath("commonjs.ts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from CommonJS TypeScript!/);
+	strictEqual(result.code, 0);
+});
+
+test("should work with .cts files using strip", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-strip.mjs",
+		fixturesPath("commonjs.cts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from CommonJS TypeScript \(\.cts\)!/);
+	strictEqual(result.code, 0);
+});
+
+test("should work with .cts files using transform", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-transform.mjs",
+		fixturesPath("commonjs.cts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from CommonJS TypeScript \(\.cts\)!/);
+	strictEqual(result.code, 0);
+});
+
+test("should work with esm typescript files using strip", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-strip.mjs",
+		fixturesPath("esm/esm.ts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from ESM TypeScript!/);
+	strictEqual(result.code, 0);
+});
+
+test("should work with esm typescript files using transform", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-transform.mjs",
+		fixturesPath("esm/esm.ts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from ESM TypeScript!/);
+	strictEqual(result.code, 0);
+});
+
+test("should work with .mts files using strip", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-strip.mjs",
+		fixturesPath("esm.mts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from ESM TypeScript!/);
+	strictEqual(result.code, 0);
+});
+
+test("should work with .mts files using transform", async () => {
+	const result = await spawnPromisified(process.execPath, [
+		"--no-warnings",
+		"--import=./dist/register-transform.mjs",
+		fixturesPath("esm.mts"),
+	]);
+
+	strictEqual(result.stderr, "");
+	match(result.stdout, /Hello from ESM TypeScript!/);
+	strictEqual(result.code, 0);
+});