diff --git a/src/media/mime.test.ts b/src/media/mime.test.ts
index 020364663fb..2042ac8b823 100644
--- a/src/media/mime.test.ts
+++ b/src/media/mime.test.ts
@@ -60,6 +60,13 @@ describe("mime detection", () => {
     });
     expect(mime).toBe("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
   });
+
+  it("uses extension mapping for JavaScript assets", async () => {
+    const mime = await detectMime({
+      filePath: "/tmp/a2ui.bundle.js",
+    });
+    expect(mime).toBe("text/javascript");
+  });
 });
 
 describe("extensionForMime", () => {
diff --git a/src/media/mime.ts b/src/media/mime.ts
index 6a377b7dc6e..85f4962b43d 100644
--- a/src/media/mime.ts
+++ b/src/media/mime.ts
@@ -38,6 +38,7 @@ const MIME_BY_EXT: Record<string, string> = {
   ...Object.fromEntries(Object.entries(EXT_BY_MIME).map(([mime, ext]) => [ext, mime])),
   // Additional extension aliases
   ".jpeg": "image/jpeg",
+  ".js": "text/javascript",
 };
 
 const AUDIO_FILE_EXTENSIONS = new Set([