> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/0001-to-0023/aur0021.md).

# AUR0021

### **Error message**

Invalid module transform input: yyyy. Expected Promise or Object.

### **Parameters**

Input value (any)

### Error explanation

This error occurs when a module loader or transformer receives an input that is neither a Promise nor an Object. The module loader expects to work with either a module object or a Promise that resolves to a module, and will throw this error if given an invalid type (such as a string, number, or null).

### Common causes

* Passing a primitive value (string, number, boolean, etc.) instead of a module or Promise to a module loader or transformer.
* Accidentally passing `null` or `undefined` as the input.
* Misconfigured dynamic import or require call.

### How to fix

* Ensure you are passing either a module object or a Promise that resolves to a module.
* Check the value being passed to the module loader or transformer for typos or incorrect types.
* If using dynamic imports, verify that the import or require call returns a Promise or module object.

### Debugging tips

* Check the stack trace to see where the invalid input was provided.
* Add logging or breakpoints to inspect the value being passed to the module loader or transformer.
* Review the code that constructs or imports modules to ensure correct types are used.


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