> For the complete documentation index, see [llms.txt](https://docs.create-scandipwa-app.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.create-scandipwa-app.com/extensions/virtual-modules.md).

# Module preference

ScandiPWA introduces concept of module preference. **This is a feature of** [**ScandiPWA extensions**](/extensions/extensions.md). 

{% hint style="info" %}
**To preference a module** - to take-over another NPM or virtual module. To take-over means to completely replace an implementation, the original module will not be available.
{% endhint %}

To preference a module, set the `scandipwa.preference`  field of `package.json` equal to the desired module name.

{% hint style="danger" %}

### Watch out!

This is very dangerous to preference a real NPM module, like in example `react` or `redux`. While you can do this, this feature is meant for [virtual module preference](/extensions/extensions.md#virtual-module-preference).
{% endhint %}

###  Virtual module preference

{% hint style="danger" %}

### Watch out!

This is a subject to change. We plan on providing a more robust way to depend on virtual modules. **They should be coupled with typescript interfaces**. Currently, virtual-modules only work on the level of module resolution, they do not provide any interface for the implementation. 
{% endhint %}

Create ScandiPWA App introduces the concept of "virtual module".

{% hint style="info" %}
**Virtual module** - a non-existing module, referenced in the code. It provides an abstraction layer, which allows to swap the implementation.
{% endhint %}

Virtual modules are useful for UI elements, where different libraries could be used as an implementation, or for an API endpoints, where the application is relying on data format, not the source of the data.

To create a virtual module, define the reference to a non existing module, and [implement a preference](/extensions/extensions.md#extension-module-preference) in your extension to it. To ensure that it does not exist, use `@virtual-module/<name>` name for it.


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