fix: guard esm module

Author: floydspace

src/index.ts

@@ -36,6 +36,7 @@ import type {
   ReturnPluginsFn,
   ESMPluginsModule,
 } from './types';
+import { isESMModule } from './utils';
 
 function updateFile(op: string, src: string, dest: string) {
   if (['add', 'change', 'addDir'].includes(op)) {
@@ -255,11 +256,12 @@ class EsbuildServerlessPlugin implements ServerlessPlugin {
       return this.buildOptions.plugins;
     }
 
-    let plugins: Plugins | ReturnPluginsFn | ESMPluginsModule = require(
-      path.join(this.serviceDirPath, this.buildOptions.plugins)
-    );
+    let plugins: Plugins | ReturnPluginsFn | ESMPluginsModule = require(path.join(
+      this.serviceDirPath,
+      this.buildOptions.plugins
+    ));
 
-    if (plugins.default) {
+    if (isESMModule(plugins)) {
       plugins = plugins.default;
     }
 

src/utils.ts

@@ -6,7 +6,7 @@ import { type Cause, Effect, Option } from 'effect';
 import execa from 'execa';
 import fs from 'fs-extra';
 import path from 'path';
-import type { IFile, IFiles } from './types';
+import type { ESMPluginsModule, IFile, IFiles } from './types';
 import FS, { FSyncLayer, makePath, makeTempPathScoped, safeFileExists } from './utils/effect-fs';
 
 export class SpawnError extends Error {
@@ -135,3 +135,7 @@ export const isEmpty = (obj: Record<string, unknown>) => {
 
   return true;
 };
+
+export const isESMModule = (obj: unknown): obj is ESMPluginsModule => {
+  return typeof obj === 'object' && obj !== null && 'default' in obj;
+};