feat: support es3 target (#965)

src/index.ts

@@ -16,7 +16,7 @@ import { runEsbuild } from './esbuild'
 import { shebang } from './plugins/shebang'
 import { cjsSplitting } from './plugins/cjs-splitting'
 import { PluginContainer } from './plugin'
-import { es5 } from './plugins/es5'
+import { swcTarget } from './plugins/swc-target'
 import { sizeReporter } from './plugins/size-reporter'
 import { treeShakingPlugin } from './plugins/tree-shaking'
 import { copyPublicDir, isInPublicDir } from './lib/public-dir'
@@ -256,7 +256,7 @@ export async function build(_options: Options) {
                     }),
                     cjsSplitting(),
                     cjsInterop(),
-                    es5(),
+                    swcTarget(),
                     sizeReporter(),
                     terserPlugin({
                       minifyOptions: options.minify,

src/plugins/swc-target.ts

@@ -0,0 +1,65 @@
+import { PrettyError } from '../errors'
+import { Plugin } from '../plugin'
+import { localRequire } from '../utils'
+
+const TARGETS = ['es5', 'es3'] as const
+
+export const swcTarget = (): Plugin => {
+  let enabled = false
+  let target: typeof TARGETS[number]
+
+  return {
+    name: 'swc-target',
+
+    esbuildOptions(options) {
+      if (
+        typeof options.target === 'string' &&
+        TARGETS.includes(options.target as any)
+      ) {
+        target = options.target as any
+        options.target = 'es2020'
+        enabled = true
+      }
+    },
+
+    async renderChunk(code, info) {
+      if (!enabled || !/\.(cjs|js)$/.test(info.path) || this.format !== 'cjs') {
+        return
+      }
+      const swc: typeof import('@swc/core') = localRequire('@swc/core')
+
+      if (!swc) {
+        throw new PrettyError(
+          `@swc/core is required for ${target} target. Please install it with \`npm install @swc/core -D\``
+        )
+      }
+
+      const result = await swc.transform(code, {
+        filename: info.path,
+        sourceMaps: this.options.sourcemap,
+        minify: Boolean(this.options.minify),
+        jsc: {
+          target,
+          parser: {
+            syntax: 'ecmascript',
+          },
+          minify:
+            this.options.minify === true
+              ? {
+                  compress: false,
+                  mangle: {
+                    reserved: this.options.globalName
+                      ? [this.options.globalName]
+                      : [],
+                  },
+                }
+              : undefined,
+        },
+      })
+      return {
+        code: result.code,
+        map: result.map,
+      }
+    },
+  }
+}