[Home](./index.md) > [@firebase/performance](./performance.md) > [initializePerformance](./performance.initializeperformance.md) ## initializePerformance() function Returns a FirebasePerformance instance for the given app. Can only be called once. Signature: ```typescript export declare function initializePerformance(app: FirebaseApp, settings?: PerformanceSettings): FirebasePerformance; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | app | [FirebaseApp](./app.firebaseapp.md) | The FirebaseApp to use. | | settings | [PerformanceSettings](./performance.performancesettings.md) | Optional settings for the FirebasePerformance instance. | Returns: [FirebasePerformance](./performance.firebaseperformance.md)