[Home](./index.md) > [@firebase/functions](./functions.md) > [Functions](./functions.functions.md) ## Functions interface `Functions` represents a Functions instance, and is a required argument for all Functions operations. Signature: ```typescript export interface Functions ``` ## Properties | Property | Type | Description | | --- | --- | --- | | [app](./functions.functions.app.md) | [FirebaseApp](./app.firebaseapp.md) | The FirebaseApp this Functions instance is associated with. | | [customDomain](./functions.functions.customdomain.md) | string \| null | A custom domain hosting the callable Cloud Functions. ex: https://mydomain.com | | [region](./functions.functions.region.md) | string | The region the callable Cloud Functions are located in. Default is us-central-1. |