__name issues

When using the OpenNext adapter, Wrangler processes the worker's code with esbuild (opens in a new tab), and by default enables the keep-names (opens in a new tab) option. While this is generally useful for debugging, it can cause issues with certain Next.js libraries (e.g. next-themes (opens in a new tab)) that convert scripts to strings. This happens because esbuild introduces a __name function at the top of modules, which may inadvertently appear in the generated script strings. When these strings are evaluated at runtime, the __name function might therefore not be defined, leading to errors logged in the developper console:

Uncaught ReferenceError: __name is not defined

How to fix such issues

To fix the issue you can simply set the keep_names option to false in your wrangler.jsonc file (opens in a new tab), like in the following example:

{
  "$schema": "node_modules/wrangler/config-schema.json",
  "main": ".open-next/worker.js",
  "name": "my-app",
  "keep_names": false,
  /* ... */
}

One potential drawback of this solution is that, depending on your minification settings, you may lose the ability to view the original function names in debugging tools.