fix(legacy): use swc to transform esm to es3

lib/esbuild.config.js

@@ -3,6 +3,8 @@ import { fileURLToPath } from 'url';
 
 import { build, context, analyzeMetafile } from 'esbuild';
 import * as dotenv from 'dotenv';
+import swc from '@swc/core';
+import { promises as fs } from 'fs';
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
@@ -44,43 +46,53 @@ const config = {
   sourcemap: BUILD === 'development',
 };
 
+const swcOptions = {
+  minify: true,
+  sourceMaps: true,
+  jsc: {
+    target: 'es3',
+  },
+};
+
 
 if (WATCH) {
   const ctx = await context({
     ...config,
     format: 'esm',
     outfile: resolve(DIST, 'index.mjs'),
     treeShaking: true,
-    target: [
-      'es6'
-    ]
   });
   await ctx.watch();
 } else {
+  // Transpile TypeScript to ESM
   const resultESM = await build({
     ...config,
     format: 'esm',
-    outfile: resolve(DIST, 'index.mjs'),
+    outfile: resolve(DIST, 'index.js'),
     treeShaking: true,
-    target: [
-      'es6'
-    ]
   });
 
+  // Transpile TypeScript to CommonJS
   const resultCJS = await build({
     ...config,
     format: 'cjs',
     outfile: resolve(DIST, 'index.cjs'),
-    treeShaking: true
+    treeShaking: true,
   });
 
+  // Transform ESM to ES3
+  const resultES3 = await swc.transformFile(resolve(DIST, 'index.js'), swcOptions);
+  await fs.writeFile(resolve(DIST, 'index.mjs'), resultES3.code, 'utf-8');
+  await fs.writeFile(resolve(DIST, 'index.mjs.map'), resultES3.map, 'utf-8');
+
   if (DEBUG) {
     const analyzeESM = await analyzeMetafile(resultESM.metafile, {
       verbose: false
     });
     const analyzeCJS = await analyzeMetafile(resultCJS.metafile, {
       verbose: false
     });
+
     console.log(analyzeESM);
     console.log(analyzeCJS);
   }