[Home](./index.md) > [@firebase/app](./app.md) > [onLog](./app.onlog.md) ## onLog() function Sets log handler for all Firebase SDKs. Signature: ```typescript export declare function onLog(logCallback: LogCallback | null, options?: LogOptions): void; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | logCallback | LogCallback \| null | An optional custom log handler that executes user code whenever the Firebase SDK makes a logging call. | | options | LogOptions | | Returns: void