diff --git a/package-lock.json b/package-lock.json
index 543f882..96b8006 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -54,6 +54,7 @@
         "svelte": "3.37.0",
         "ts-essentials": "^7.0.1",
         "ts-jest": "^26.5.5",
+        "tsup": "^5.7.2",
         "typescript": "^4.2.4",
         "wait-for-expect": "^3.0.2"
       },
@@ -6733,6 +6734,39 @@
         "node": ">=10"
       }
     },
+    "node_modules/tsup": {
+      "version": "5.7.2",
+      "resolved": "https://registry.npmjs.org/tsup/-/tsup-5.7.2.tgz",
+      "integrity": "sha512-YxryYjhB54h8YUNlN7Oze9PnqcuN++vwrFW6qtjC1ve9eQPvzCJw0rN0WPOuEQXburwo+gtDid9C4eQZ6x/Yog==",
+      "dev": true,
+      "dependencies": {
+        "cac": "^6.7.2",
+        "chalk": "^4.1.0",
+        "chokidar": "^3.5.1",
+        "debug": "^4.3.1",
+        "esbuild": "^0.13.4",
+        "execa": "^5.0.0",
+        "globby": "^11.0.3",
+        "joycon": "^3.0.1",
+        "postcss-load-config": "^3.0.1",
+        "resolve-from": "^5.0.0",
+        "rollup": "^2.56.1",
+        "sucrase": "^3.20.1",
+        "tree-kill": "^1.2.2"
+      },
+      "bin": {
+        "tsup": "dist/cli-default.js",
+        "tsup-node": "dist/cli-node.js"
+      },
+      "peerDependencies": {
+        "typescript": "^4.2.3"
+      },
+      "peerDependenciesMeta": {
+        "typescript": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/type-check": {
       "version": "0.3.2",
       "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.3.2.tgz",
@@ -12380,6 +12414,27 @@
         }
       }
     },
+    "tsup": {
+      "version": "5.7.2",
+      "resolved": "https://registry.npmjs.org/tsup/-/tsup-5.7.2.tgz",
+      "integrity": "sha512-YxryYjhB54h8YUNlN7Oze9PnqcuN++vwrFW6qtjC1ve9eQPvzCJw0rN0WPOuEQXburwo+gtDid9C4eQZ6x/Yog==",
+      "dev": true,
+      "requires": {
+        "cac": "^6.7.2",
+        "chalk": "^4.1.0",
+        "chokidar": "^3.5.1",
+        "debug": "^4.3.1",
+        "esbuild": "^0.13.4",
+        "execa": "^5.0.0",
+        "globby": "^11.0.3",
+        "joycon": "^3.0.1",
+        "postcss-load-config": "^3.0.1",
+        "resolve-from": "^5.0.0",
+        "rollup": "^2.56.1",
+        "sucrase": "^3.20.1",
+        "tree-kill": "^1.2.2"
+      }
+    },
     "type-check": {
       "version": "0.3.2",
       "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.3.2.tgz",
diff --git a/package.json b/package.json
index d03dbc4..019e4bc 100644
--- a/package.json
+++ b/package.json
@@ -18,12 +18,11 @@
   },
   "scripts": {
     "dev": "npm run build:simple -- --watch",
-    "build": "npm run tsup -- src/cli-*.ts src/index.ts src/rollup.ts --clean --dts-resolve --splitting",
+    "build": "tsup src/cli-*.ts src/index.ts src/rollup.ts --clean --dts-resolve --splitting",
     "prepublishOnly": "npm run build",
     "test": "npm run build:simple && jest",
     "//": "Building without dts for speed",
-    "build:simple": "npm run tsup -- src/cli-*.ts src/index.ts src/rollup.ts --clean --splitting",
-    "tsup": "node -r sucrase/register src/cli-default.ts"
+    "build:simple": "tsup src/cli-*.ts src/index.ts src/rollup.ts --clean --splitting"
   },
   "dependencies": {
     "cac": "^6.7.2",
@@ -67,6 +66,7 @@
     "svelte": "3.37.0",
     "ts-essentials": "^7.0.1",
     "ts-jest": "^26.5.5",
+    "tsup": "^5.7.2",
     "typescript": "^4.2.4",
     "wait-for-expect": "^3.0.2"
   },
diff --git a/src/esbuild/index.ts b/src/esbuild/index.ts
new file mode 100644
index 0000000..c13447f
--- /dev/null
+++ b/src/esbuild/index.ts
@@ -0,0 +1,257 @@
+import fs from 'fs'
+import path from 'path'
+import type { InputOption } from 'rollup'
+import { transform as transformToEs5 } from 'buble'
+import {
+  build as esbuild,
+  BuildOptions,
+  BuildResult,
+  Plugin as EsbuildPlugin,
+  formatMessages,
+} from 'esbuild'
+import { NormalizedOptions, Format } from '..'
+import { getDeps, loadPkg } from '../load'
+import { log } from '../log'
+import { externalPlugin } from './external'
+import { postcssPlugin } from './postcss'
+import { sveltePlugin } from './svelte'
+import consola from 'consola'
+import { getBabel } from '../utils'
+import { PrettyError } from '../errors'
+import { transform } from 'sucrase'
+
+const getOutputExtensionMap = (
+  pkgTypeField: string | undefined,
+  format: Format
+) => {
+  const isModule = pkgTypeField === 'module'
+  const map: any = {}
+  if (isModule && format === 'cjs') {
+    map['.js'] = '.cjs'
+  }
+  if (!isModule && format === 'esm') {
+    map['.js'] = '.mjs'
+  }
+  if (format === 'iife') {
+    map['.js'] = '.global.js'
+  }
+  return map
+}
+
+export async function runEsbuild(
+  options: NormalizedOptions,
+  { format, css }: { format: Format; css?: Map<string, string> }
+) {
+  const pkg = await loadPkg(process.cwd())
+  const deps = await getDeps(process.cwd())
+  const external = [
+    // Exclude dependencies, e.g. `lodash`, `lodash/get`
+    ...deps.map((dep) => new RegExp(`^${dep}($|\\/|\\\\)`)),
+    ...(options.external || []),
+  ]
+  const outDir = options.outDir
+
+  const outExtension = getOutputExtensionMap(pkg.type, format)
+  const env: { [k: string]: string } = {
+    ...options.env,
+  }
+
+  if (options.replaceNodeEnv) {
+    env.NODE_ENV =
+      options.minify || options.minifyWhitespace ? 'production' : 'development'
+  }
+
+  log(format, 'info', 'Build start')
+
+  const startTime = Date.now()
+
+  let result: BuildResult | undefined
+
+  const splitting =
+    format === 'iife'
+      ? false
+      : typeof options.splitting === 'boolean'
+      ? options.splitting
+      : format === 'esm'
+
+  const platform = options.platform || 'node'
+
+  try {
+    result = await esbuild({
+      entryPoints: options.entryPoints,
+      format: format === 'cjs' && splitting ? 'esm' : format,
+      bundle: typeof options.bundle === 'undefined' ? true : options.bundle,
+      platform,
+      globalName: options.globalName,
+      jsxFactory: options.jsxFactory,
+      jsxFragment: options.jsxFragment,
+      sourcemap: options.sourcemap,
+      target: options.target === 'es5' ? 'es2016' : options.target,
+      footer: options.footer,
+      banner: options.banner,
+      mainFields:
+        platform === 'node'
+          ? ['module', 'main']
+          : ['browser', 'module', 'main'],
+      plugins: [
+        {
+          name: 'modify-options',
+          setup(build) {
+            if (options.esbuildOptions) {
+              options.esbuildOptions(build.initialOptions, { format })
+            }
+          },
+        },
+        // esbuild's `external` option doesn't support RegExp
+        // So here we use a custom plugin to implement it
+        externalPlugin({
+          // everything should be bundled for iife format
+          disabled: format === 'iife',
+          patterns: external,
+          skipNodeModulesBundle: options.skipNodeModulesBundle,
+        }),
+        postcssPlugin({ css }),
+        sveltePlugin({ css }),
+        ...(options.esbuildPlugins || []),
+      ],
+      define: {
+        ...(format === 'cjs'
+          ? {
+              'import.meta.url': 'importMetaUrlShim',
+            }
+          : {}),
+        ...options.define,
+        ...Object.keys(env).reduce((res, key) => {
+          const value = JSON.stringify(env[key])
+          return {
+            ...res,
+            [`process.env.${key}`]: value,
+            [`import.meta.env.${key}`]: value,
+          }
+        }, {}),
+      },
+      inject: [
+        format === 'cjs' ? path.join(__dirname, '../assets/cjs_shims.js') : '',
+        ...(options.inject || []),
+      ].filter(Boolean),
+      outdir:
+        options.legacyOutput && format !== 'cjs'
+          ? path.join(outDir, format)
+          : outDir,
+      outExtension: options.legacyOutput ? undefined : outExtension,
+      write: false,
+      splitting,
+      logLevel: 'error',
+      minify: options.minify,
+      minifyWhitespace: options.minifyWhitespace,
+      minifyIdentifiers: options.minifyIdentifiers,
+      minifySyntax: options.minifySyntax,
+      keepNames: options.keepNames,
+      incremental: !!options.watch,
+      pure: typeof options.pure === 'string' ? [options.pure] : options.pure,
+      metafile: Boolean(options.metafile),
+    })
+  } catch (error) {
+    log(format, 'error', 'Build failed')
+    throw error
+  }
+
+  if (result && result.warnings) {
+    const messages = result.warnings.filter((warning) => {
+      if (
+        warning.text.includes(
+          `This call to "require" will not be bundled because`
+        ) ||
+        warning.text.includes(`Indirect calls to "require" will not be bundled`)
+      )
+        return false
+
+      return true
+    })
+    const formatted = await formatMessages(messages, {
+      kind: 'warning',
+      color: true,
+    })
+    formatted.forEach((message) => {
+      consola.warn(message)
+    })
+  }
+
+  // Manually write files
+  if (result && result.outputFiles) {
+    const timeInMs = Date.now() - startTime
+    log(format, 'success', `Build success in ${Math.floor(timeInMs)}ms`)
+
+    await Promise.all(
+      result.outputFiles.map(async (file) => {
+        const dir = path.dirname(file.path)
+        const outPath = file.path
+        const ext = path.extname(outPath)
+        const comeFromSource = ext === '.js' || ext === outExtension['.js']
+        await fs.promises.mkdir(dir, { recursive: true })
+        let contents = file.text
+        let mode: number | undefined
+        if (contents[0] === '#' && contents[1] === '!') {
+          mode = 0o755
+        }
+        if (comeFromSource) {
+          if (options.babel) {
+            const babel = getBabel()
+            if (babel) {
+              contents = await babel
+                .transformAsync(contents, {
+                  filename: file.path,
+                })
+                .then((res) => res?.code || contents)
+            } else {
+              throw new PrettyError(
+                `@babel/core is not found in ${process.cwd()}`
+              )
+            }
+          }
+          if (options.target === 'es5') {
+            try {
+              contents = transformToEs5(contents, {
+                source: file.path,
+                file: file.path,
+                transforms: {
+                  modules: false,
+                  arrow: true,
+                  dangerousTaggedTemplateString: true,
+                  spreadRest: true,
+                },
+              }).code
+            } catch (error: any) {
+              throw new PrettyError(
+                `Error compiling to es5 target:\n${error.snippet}`
+              )
+            }
+          }
+          // Workaround to enable code splitting for cjs format
+          // Manually transform esm to cjs
+          // TODO: remove this once esbuild supports code splitting for cjs natively
+          if (splitting && format === 'cjs') {
+            contents = transform(contents, {
+              filePath: file.path,
+              transforms: ['imports'],
+            }).code
+          }
+        }
+        await fs.promises.writeFile(outPath, contents, {
+          encoding: 'utf8',
+          mode,
+        })
+      })
+    )
+  }
+
+  if (options.metafile && result?.metafile) {
+    const outPath = path.resolve(outDir, `metafile-${format}.json`)
+    await fs.promises.mkdir(path.dirname(outPath), { recursive: true })
+    await fs.promises.writeFile(
+      outPath,
+      JSON.stringify(result.metafile),
+      'utf8'
+    )
+  }
+}
diff --git a/src/index.ts b/src/index.ts
index b1fb493..14258e6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,33 +1,20 @@
+import path from 'path'
 import fs from 'fs'
-import path, { dirname, join, extname } from 'path'
 import { Worker } from 'worker_threads'
-import type { InputOption } from 'rollup'
-import { transform as transformToEs5 } from 'buble'
-import {
-  build as esbuild,
-  BuildOptions,
-  BuildResult,
-  Plugin as EsbuildPlugin,
-  formatMessages,
-} from 'esbuild'
 import type { MarkRequired, Buildable } from 'ts-essentials'
-import { getBabel, removeFiles, debouncePromise } from './utils'
-import { getDeps, loadTsConfig, loadPkg, loadTsupConfig } from './load'
+import { removeFiles, debouncePromise } from './utils'
+import { loadTsConfig, loadTsupConfig } from './load'
 import glob from 'globby'
 import { handleError, PrettyError } from './errors'
-import { postcssPlugin } from './esbuild/postcss'
-import { externalPlugin } from './esbuild/external'
-import { sveltePlugin } from './esbuild/svelte'
 import resolveFrom from 'resolve-from'
 import { parseArgsStringToArgv } from 'string-argv'
 import type { ChildProcess } from 'child_process'
 import execa from 'execa'
-import consola from 'consola'
 import kill from 'tree-kill'
-import { transform } from 'sucrase'
 import { version } from '../package.json'
 import { log, setSilent } from './log'
 import { Format, Options } from './options'
+import { runEsbuild } from './esbuild'
 
 export type { Format, Options }
 
@@ -36,24 +23,6 @@ export type NormalizedOptions = MarkRequired<
   'entryPoints' | 'format' | 'outDir'
 >
 
-const getOutputExtensionMap = (
-  pkgTypeField: string | undefined,
-  format: Format
-) => {
-  const isModule = pkgTypeField === 'module'
-  const map: any = {}
-  if (isModule && format === 'cjs') {
-    map['.js'] = '.cjs'
-  }
-  if (!isModule && format === 'esm') {
-    map['.js'] = '.mjs'
-  }
-  if (format === 'iife') {
-    map['.js'] = '.global.js'
-  }
-  return map
-}
-
 export const defineConfig = (
   options:
     | Options
@@ -63,226 +32,6 @@ export const defineConfig = (
       ) => Options)
 ) => options
 
-export async function runEsbuild(
-  options: NormalizedOptions,
-  { format, css }: { format: Format; css?: Map<string, string> }
-): Promise<BuildResult | undefined> {
-  const pkg = await loadPkg(process.cwd())
-  const deps = await getDeps(process.cwd())
-  const external = [
-    // Exclude dependencies, e.g. `lodash`, `lodash/get`
-    ...deps.map((dep) => new RegExp(`^${dep}($|\\/|\\\\)`)),
-    ...(options.external || []),
-  ]
-  const outDir = options.outDir
-
-  const outExtension = getOutputExtensionMap(pkg.type, format)
-  const env: { [k: string]: string } = {
-    ...options.env,
-  }
-
-  if (options.replaceNodeEnv) {
-    env.NODE_ENV =
-      options.minify || options.minifyWhitespace ? 'production' : 'development'
-  }
-
-  log(format, 'info', 'Build start')
-
-  const startTime = Date.now()
-
-  let result: BuildResult | undefined
-
-  const splitting =
-    format === 'iife'
-      ? false
-      : typeof options.splitting === 'boolean'
-      ? options.splitting
-      : format === 'esm'
-
-  const platform = options.platform || 'node'
-
-  try {
-    result = await esbuild({
-      entryPoints: options.entryPoints,
-      format: format === 'cjs' && splitting ? 'esm' : format,
-      bundle: typeof options.bundle === 'undefined' ? true : options.bundle,
-      platform,
-      globalName: options.globalName,
-      jsxFactory: options.jsxFactory,
-      jsxFragment: options.jsxFragment,
-      sourcemap: options.sourcemap,
-      target: options.target === 'es5' ? 'es2016' : options.target,
-      footer: options.footer,
-      banner: options.banner,
-      mainFields:
-        platform === 'node'
-          ? ['module', 'main']
-          : ['browser', 'module', 'main'],
-      plugins: [
-        {
-          name: 'modify-options',
-          setup(build) {
-            if (options.esbuildOptions) {
-              options.esbuildOptions(build.initialOptions, { format })
-            }
-          },
-        },
-        // esbuild's `external` option doesn't support RegExp
-        // So here we use a custom plugin to implement it
-        externalPlugin({
-          // everything should be bundled for iife format
-          disabled: format === 'iife',
-          patterns: external,
-          skipNodeModulesBundle: options.skipNodeModulesBundle,
-        }),
-        postcssPlugin({ css }),
-        sveltePlugin({ css }),
-        ...(options.esbuildPlugins || []),
-      ],
-      define: {
-        ...(format === 'cjs'
-          ? {
-              'import.meta.url': 'importMetaUrlShim',
-            }
-          : {}),
-        ...options.define,
-        ...Object.keys(env).reduce((res, key) => {
-          const value = JSON.stringify(env[key])
-          return {
-            ...res,
-            [`process.env.${key}`]: value,
-            [`import.meta.env.${key}`]: value,
-          }
-        }, {}),
-      },
-      inject: [
-        format === 'cjs' ? join(__dirname, '../assets/cjs_shims.js') : '',
-        ...(options.inject || []),
-      ].filter(Boolean),
-      outdir:
-        options.legacyOutput && format !== 'cjs'
-          ? join(outDir, format)
-          : outDir,
-      outExtension: options.legacyOutput ? undefined : outExtension,
-      write: false,
-      splitting,
-      logLevel: 'error',
-      minify: options.minify,
-      minifyWhitespace: options.minifyWhitespace,
-      minifyIdentifiers: options.minifyIdentifiers,
-      minifySyntax: options.minifySyntax,
-      keepNames: options.keepNames,
-      incremental: !!options.watch,
-      pure: typeof options.pure === 'string' ? [options.pure] : options.pure,
-      metafile: Boolean(options.metafile),
-    })
-  } catch (error) {
-    log(format, 'error', 'Build failed')
-    throw error
-  }
-
-  if (result && result.warnings) {
-    const messages = result.warnings.filter((warning) => {
-      if (
-        warning.text.includes(
-          `This call to "require" will not be bundled because`
-        ) ||
-        warning.text.includes(`Indirect calls to "require" will not be bundled`)
-      )
-        return false
-
-      return true
-    })
-    const formatted = await formatMessages(messages, {
-      kind: 'warning',
-      color: true,
-    })
-    formatted.forEach((message) => {
-      consola.warn(message)
-    })
-  }
-
-  // Manually write files
-  if (result && result.outputFiles) {
-    const timeInMs = Date.now() - startTime
-    log(format, 'success', `Build success in ${Math.floor(timeInMs)}ms`)
-
-    await Promise.all(
-      result.outputFiles.map(async (file) => {
-        const dir = dirname(file.path)
-        const outPath = file.path
-        const ext = extname(outPath)
-        const comeFromSource = ext === '.js' || ext === outExtension['.js']
-        await fs.promises.mkdir(dir, { recursive: true })
-        let contents = file.text
-        let mode: number | undefined
-        if (contents[0] === '#' && contents[1] === '!') {
-          mode = 0o755
-        }
-        if (comeFromSource) {
-          if (options.babel) {
-            const babel = getBabel()
-            if (babel) {
-              contents = await babel
-                .transformAsync(contents, {
-                  filename: file.path,
-                })
-                .then((res) => res?.code || contents)
-            } else {
-              throw new PrettyError(
-                `@babel/core is not found in ${process.cwd()}`
-              )
-            }
-          }
-          if (options.target === 'es5') {
-            try {
-              contents = transformToEs5(contents, {
-                source: file.path,
-                file: file.path,
-                transforms: {
-                  modules: false,
-                  arrow: true,
-                  dangerousTaggedTemplateString: true,
-                  spreadRest: true,
-                },
-              }).code
-            } catch (error: any) {
-              throw new PrettyError(
-                `Error compiling to es5 target:\n${error.snippet}`
-              )
-            }
-          }
-          // Workaround to enable code splitting for cjs format
-          // Manually transform esm to cjs
-          // TODO: remove this once esbuild supports code splitting for cjs natively
-          if (splitting && format === 'cjs') {
-            contents = transform(contents, {
-              filePath: file.path,
-              transforms: ['imports'],
-            }).code
-          }
-        }
-        await fs.promises.writeFile(outPath, contents, {
-          encoding: 'utf8',
-          mode,
-        })
-      })
-    )
-  }
-
-  if (options.metafile && result?.metafile) {
-    const outPath = path.resolve(outDir, `metafile-${format}.json`)
-    await fs.promises.mkdir(path.dirname(outPath), { recursive: true })
-    await fs.promises.writeFile(
-      outPath,
-      JSON.stringify(result.metafile),
-      'utf8'
-    )
-  }
-
-  return result
-}
-
 const killProcess = ({
   pid,
   signal = 'SIGTERM',
@@ -484,10 +233,7 @@ export async function build(_options: Options) {
       throw new Error(`You need to install "typescript" in your project`)
     }
 
-    const isDev = __filename.endsWith('index.ts')
-    const worker = new Worker(
-      join(__dirname, isDev ? './rollup.dev.js' : './rollup.js')
-    )
+    const worker = new Worker(path.join(__dirname, './rollup.js'))
     worker.postMessage({
       options: {
         ...options, // functions cannot be cloned
diff --git a/src/rollup.dev.js b/src/rollup.dev.js
deleted file mode 100644
index d470259..0000000
--- a/src/rollup.dev.js
+++ /dev/null
@@ -1 +0,0 @@
-import './rollup'