@snap/camera-kit/docs/md/functions/createExtension.md

Camera Kit Web

[**CameraKit Web SDK v1.4.0**](../README.md)

***

[CameraKit Web SDK](../globals.md) / createExtension

# Function: createExtension()

> **createExtension**(): `PartialContainer`

Extensions offer a way to provide custom implementations of certain parts of the CameraKit SDK.

This enables more advanced use-cases, in which the default behavior of the SDK is substantially altered. For example,
replacing the default implementation that loads remote lens assets with a custom implementation that returns
different assets based on some business logic within the application.

An extension is implemented as a PartialContainer – a collection of factory functions, each with its own
dependencies, which each provide some "Service". A Service can be of any type, and the CameraKit SDK defines its
own Services, some of which can be overridden by providing a custom implementation of the type via an extension.

Here's an example of how extensions might be used:
```ts
import { bootstrapCameraKit, createExtension, remoteMediaAssetLoaderFactory } from '@snap/camera-kit'

const myCustomRemoteAssetLoader = Injectable(
  remoteMediaAssetLoaderFactory.token,
  [remoteMediaAssetLoaderFactory.token] as const,
  (defaultLoader: AssetLoader): AssetLoader => {
    return async (asset, lens) => {
      if (lens?.id === MY_SPECIAL_LENS) {
        return (await fetch('my/asset.glb')).arrayBuffer()
      }
      return defaultLoader(asset, lens)
    }
  },
)

const myExtension = createExtension().provides(myCustomRemoteAssetLoader);
const cameraKit = bootstrapCameraKit(config, container => container.provides(myExtension));
```

This also enables greater modularity – the person/team creating the extension can do so in their own package, which
could be shared by many applications that all require the same functionality.

## Returns

`PartialContainer`

A PartialContainer which can be used to create a collection of Services, and can later be provided
to CameraKit's DI container during [bootstrapCameraKit](bootstrapCameraKit.md).