From 2b13547a5f72f033bf300fb737b84252a98fe9b4 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Mon, 18 May 2026 16:30:36 +0900
Subject: [PATCH] fix: apply cjs interop for truthy `__esModule` (#10363)

---
 .../runtime/moduleRunner/moduleEvaluator.ts   |  2 +-
 test/unit/deps/dep-cjs/esmodule-false.js      |  2 +
 test/unit/deps/dep-cjs/esmodule.js            |  2 +
 test/unit/deps/dep-cjs/package.json           |  2 +
 test/unit/test/interop.test.ts                | 44 +++++++++++++++++++
 5 files changed, 51 insertions(+), 1 deletion(-)
 create mode 100644 test/unit/deps/dep-cjs/esmodule-false.js
 create mode 100644 test/unit/deps/dep-cjs/esmodule.js
 create mode 100644 test/unit/test/interop.test.ts

diff --git a/packages/vitest/src/runtime/moduleRunner/moduleEvaluator.ts b/packages/vitest/src/runtime/moduleRunner/moduleEvaluator.ts
index 297840c70c67..9fc24fd352f7 100644
--- a/packages/vitest/src/runtime/moduleRunner/moduleEvaluator.ts
+++ b/packages/vitest/src/runtime/moduleRunner/moduleEvaluator.ts
@@ -531,7 +531,7 @@ function interopModule(mod: any) {
 
   let defaultExport = 'default' in mod ? mod.default : mod
 
-  if (!isPrimitive(defaultExport) && '__esModule' in defaultExport) {
+  if (!isPrimitive(defaultExport) && defaultExport.__esModule) {
     mod = defaultExport
     if ('default' in defaultExport) {
       defaultExport = defaultExport.default
diff --git a/test/unit/deps/dep-cjs/esmodule-false.js b/test/unit/deps/dep-cjs/esmodule-false.js
new file mode 100644
index 000000000000..a9fdd6494cfd
--- /dev/null
+++ b/test/unit/deps/dep-cjs/esmodule-false.js
@@ -0,0 +1,2 @@
+exports.__esModule = false
+exports.test = 'hello'
diff --git a/test/unit/deps/dep-cjs/esmodule.js b/test/unit/deps/dep-cjs/esmodule.js
new file mode 100644
index 000000000000..6d1bd23dd125
--- /dev/null
+++ b/test/unit/deps/dep-cjs/esmodule.js
@@ -0,0 +1,2 @@
+exports.__esModule = true
+exports.test = 'hello'
diff --git a/test/unit/deps/dep-cjs/package.json b/test/unit/deps/dep-cjs/package.json
index f424b60c62fb..1d7e46883ea9 100644
--- a/test/unit/deps/dep-cjs/package.json
+++ b/test/unit/deps/dep-cjs/package.json
@@ -2,6 +2,8 @@
   "name": "@vitest/test-dep-cjs",
   "type": "commonjs",
   "exports": {
+    "./esmodule": "./esmodule.js",
+    "./esmodule-false": "./esmodule-false.js",
     "./esm-comment": "./esm-comment.js",
     "./esm-string": "./esm-string.js"
   }
diff --git a/test/unit/test/interop.test.ts b/test/unit/test/interop.test.ts
new file mode 100644
index 000000000000..88709c220b0c
--- /dev/null
+++ b/test/unit/test/interop.test.ts
@@ -0,0 +1,44 @@
+// @ts-expect-error no type
+import * as esModule from '@vitest/test-dep-cjs/esmodule'
+// @ts-expect-error no type
+import * as esModuleFalse from '@vitest/test-dep-cjs/esmodule-false'
+import { expect, test } from 'vitest'
+
+const nodeMajor = Number(process.versions.node.split('.')[0])
+
+test('interop', async ({ task }) => {
+  expect(esModule).toMatchInlineSnapshot(`
+    {
+      "__esModule": true,
+      "test": "hello",
+    }
+  `)
+  if (task.file.projectName === 'vmThreads' || nodeMajor < 23) {
+    expect(esModuleFalse).toMatchInlineSnapshot(`
+      {
+        "__esModule": false,
+        "default": {
+          "__esModule": false,
+          "test": "hello",
+        },
+        "test": "hello",
+      }
+    `)
+  }
+  else {
+    expect(esModuleFalse).toMatchInlineSnapshot(`
+      {
+        "__esModule": false,
+        "default": {
+          "__esModule": false,
+          "test": "hello",
+        },
+        "module.exports": {
+          "__esModule": false,
+          "test": "hello",
+        },
+        "test": "hello",
+      }
+    `)
+  }
+})