[Home](./index.md) > [@firebase/firestore](./firestore.md) > [/](./firestore_.md) > [useFirestoreEmulator](./firestore_.usefirestoreemulator.md) ## useFirestoreEmulator() function Modify this instance to communicate with the Cloud Firestore emulator. Note: This must be called before this instance has been used to do any operations. Signature: ```typescript export declare function useFirestoreEmulator(firestore: FirebaseFirestore, host: string, port: number): void; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | firestore | [FirebaseFirestore](./firestore_.firebasefirestore.md) | The Firestore instance to configure to connect to the emulator. | | host | string | the emulator host (ex: localhost). | | port | number | the emulator port (ex: 9000). | Returns: void