unjs · momomuchu · Jul 4, 2026 · Jul 5, 2026 · Jul 5, 2026
diff --git a/src/esbuild/index.ts b/src/esbuild/index.ts
@@ -100,6 +100,7 @@ export function getEsbuildPlugin<UserOptions = Record<string, never>>(
           }
 
           let fsContentsCache: string | undefined
+          let fsContentsCached = false
 
           for (const { options, onTransformCb } of loaders) {
             if (!checkFilter(options))
@@ -113,13 +114,29 @@ export function getEsbuildPlugin<UserOptions = Record<string, never>>(
                   if (result?.contents)
                     return result.contents as string
 
-                  if (fsContentsCache)
-                    return fsContentsCache
+                  if (fsContentsCached)
+                    return fsContentsCache as string
 
                   // caution: 'utf8' assumes the input file is not in binary.
                   // if you want your plugin handle binary files, make sure to
                   // `plugin.load()` them first.
-                  return (fsContentsCache = await fs.promises.readFile(args.path, 'utf8'))
+                  try {
+                    fsContentsCache = await fs.promises.readFile(args.path, 'utf8')
+                    fsContentsCached = true
+                    return fsContentsCache
+                  }
+                  catch (error) {
+                    // esbuild resolves `package.json#browser` entries mapped to `false`
+                    // to a path that does not exist on disk (the module is meant to be
+                    // stubbed out as empty). Treat a missing file the same way esbuild
+                    // itself treats these stubs instead of throwing.
+                    if ((error as NodeJS.ErrnoException)?.code === 'ENOENT') {
+                      fsContentsCache = ''
+                      fsContentsCached = true
+                      return fsContentsCache
+                    }
+                    throw error
+                  }
                 },
               }
 

diff --git a/test/unit-tests/esbuild/fixtures/browser-false-stub/entry.js b/test/unit-tests/esbuild/fixtures/browser-false-stub/entry.js
@@ -0,0 +1 @@
+require('./pkg')
diff --git a/test/unit-tests/esbuild/fixtures/browser-false-stub/pkg/lib/index.js b/test/unit-tests/esbuild/fixtures/browser-false-stub/pkg/lib/index.js
@@ -0,0 +1,3 @@
+require('./terminal-highlight')
+
+module.exports = 'pkg-index'
diff --git a/test/unit-tests/esbuild/fixtures/browser-false-stub/pkg/package.json b/test/unit-tests/esbuild/fixtures/browser-false-stub/pkg/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "pkg",
+  "version": "1.0.0",
+  "main": "./lib/index.js",
+  "browser": {
+    "./lib/terminal-highlight": false
+  }
+}
diff --git a/test/unit-tests/esbuild/index.test.ts b/test/unit-tests/esbuild/index.test.ts
@@ -0,0 +1,72 @@
+import type { Plugin } from 'esbuild'
+import fs from 'node:fs'
+import { resolve } from 'node:path'
+import { build } from 'esbuild'
+import { describe, expect, it, vi } from 'vitest'
+import { createUnplugin } from '../../../src/index'
+
+const fixtureDir = resolve(__dirname, 'fixtures/browser-false-stub')
+
+function buildFixture(esbuildPlugin: Plugin) {
+  return build({
+    absWorkingDir: fixtureDir,
+    entryPoints: ['./entry.js'],
+    bundle: true,
+    platform: 'browser',
+    write: false,
+    plugins: [esbuildPlugin],
+  })
+}
+
+describe('esbuild getContents with browser:false stubbed module', () => {
+  it('does not throw ENOENT when transform.getContents() is called for a file switched off via package.json/browser', async () => {
+    const plugin = createUnplugin(() => ({
+      name: 'passthru',
+      transform: {
+        filter: { id: /\.[cm]?js$/ },
+        async handler(code) {
+          return { code }
+        },
+      },
+    }))
+
+    await expect(buildFixture(plugin.esbuild())).resolves.toBeDefined()
+  })
+
+  it('caches the empty contents from an ENOENT stub so a second transform does not re-read the file', async () => {
+    const readFileSpy = vi.spyOn(fs.promises, 'readFile')
+
+    try {
+      // Two transform hooks on the same plugin instance both call getContents()
+      // for the same onLoad args, exercising the shared fsContentsCache.
+      const plugin = createUnplugin(() => [
+        {
+          name: 'passthru-1',
+          transform: {
+            filter: { id: /\.[cm]?js$/ },
+            async handler(code) {
+              return { code }
+            },
+          },
+        },
+        {
+          name: 'passthru-2',
+          transform: {
+            filter: { id: /\.[cm]?js$/ },
+            async handler(code) {
+              return { code }
+            },
+          },
+        },
+      ])
+
+      await expect(buildFixture(plugin.esbuild())).resolves.toBeDefined()
+
+      const stubReads = readFileSpy.mock.calls.filter(([path]) => String(path).includes('terminal-highlight'))
+      expect(stubReads).toHaveLength(1)
+    }
+    finally {
+      readFileSpy.mockRestore()
+    }
+  })
+})
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		require('./terminal-highlight')

		module.exports = 'pkg-index'