fix: Reflect the configuration for esbuild (#12676)

.changeset/seven-feet-juggle.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Allows configuring Astro modules TypeScript compilation with the `vite.esbuild` config

packages/astro/src/vite-plugin-astro/compile.ts

@@ -37,8 +37,8 @@ export async function compileAstro({
 		// Compile all TypeScript to JavaScript.
 		// Also, catches invalid JS/TS in the compiled output before returning.
 		esbuildResult = await transformWithEsbuild(transformResult.code, compileProps.filename, {
+			...compileProps.viteConfig.esbuild,
 			loader: 'ts',
-			target: 'esnext',
 			sourcemap: 'external',
 			tsconfigRaw: {
 				compilerOptions: {

packages/astro/test/units/vite-plugin-astro/compile.test.js

@@ -5,13 +5,12 @@ import { init, parse } from 'es-module-lexer';
 import { resolveConfig } from 'vite';
 import { compileAstro } from '../../../dist/vite-plugin-astro/compile.js';
 
-const viteConfig = await resolveConfig({ configFile: false }, 'serve');
-
 /**
  * @param {string} source
  * @param {string} id
  */
-async function compile(source, id) {
+async function compile(source, id, inlineConfig = {}) {
+	const viteConfig = await resolveConfig({ configFile: false, ...inlineConfig }, 'serve');
 	return await compileAstro({
 		compileProps: {
 			astroConfig: { root: pathToFileURL('/'), base: '/', experimental: {} },
@@ -69,4 +68,24 @@ const name = 'world
 		assert.equal(names.includes('file'), true);
 		assert.equal(names.includes('url'), true);
 	});
+
+	describe('when the code contains syntax that is transformed by esbuild', () => {
+		let code = `\
+---
+using x = {}
+---`;
+
+		it('should not transform the syntax by default', async () => {
+			const result = await compile(code, '/src/components/index.astro');
+			assert.equal(result.code.includes('using x = {}'), true);
+		});
+
+		it('should transform the syntax by esbuild.target', async () => {
+			const result = await compile(code, '/src/components/index.astro', {
+				esbuild: { target: 'es2018' },
+			});
+			assert.equal(result.code.includes('using x = {}'), false);
+		});
+	});
+
 });