diff --git a/siroc.config.json b/siroc.config.json
new file mode 100644
index 0000000..7f1af14
--- /dev/null
+++ b/siroc.config.json
@@ -0,0 +1,10 @@
+{
+  "rollup": {
+    "replace": {
+      "process.env.TIME": "false"
+    },
+    "esbuildOptions": {
+      "target": "es2015"
+    }
+  }
+}
diff --git a/siroc.config.ts b/siroc.config.ts
deleted file mode 100644
index 08722c7..0000000
--- a/siroc.config.ts
+++ /dev/null
@@ -1,15 +0,0 @@
-import { defineSirocConfig, Package } from 'siroc'
-
-export default defineSirocConfig({
-  rollup: {
-    replace: {
-      'process.env.TIME': 'false',
-    },
-  },
-  hooks: {
-    'build:done'(pkg) {
-      const source = new Package({ rootDir: __dirname })
-      pkg.copyFilesFrom(source, ['README.md'])
-    },
-  },
-})
diff --git a/src/core/build/rollup.ts b/src/core/build/rollup.ts
index 6cbb976..4a8ecba 100644
--- a/src/core/build/rollup.ts
+++ b/src/core/build/rollup.ts
@@ -10,7 +10,7 @@ import nodeResolvePlugin, {
 import defu from 'defu'
 import type { RollupOptions, OutputOptions } from 'rollup'
 import dts from 'rollup-plugin-dts'
-import esbuild from 'rollup-plugin-esbuild'
+import esbuild, { Options as EsbuildOptions } from 'rollup-plugin-esbuild'
 
 import { Package } from '../package'
 import { includeDefinedProperties, includeIf } from '../utils'
@@ -30,6 +30,7 @@ export interface BuildConfigOptions extends RollupOptions {
   externals?: (string | RegExp)[]
   resolve?: RollupNodeResolveOptions
   input?: string
+  esbuildOptions?: EsbuildOptions
 }
 
 export function getRollupConfig(
@@ -44,6 +45,7 @@ export function getRollupConfig(
       preferBuiltins: true,
     },
     plugins = [],
+    esbuildOptions,
     ...options
   }: BuildConfigOptions,
   {
@@ -87,6 +89,7 @@ export function getRollupConfig(
       commonjsPlugin({ include: /node_modules/ }),
       esbuild({
         target: 'es2018',
+        ...esbuildOptions,
       }),
       jsonPlugin(),
     ].concat(plugins)