[Home](./index.md) > [ibm-cloud-sdk-core](./ibm-cloud-sdk-core.md) > [onlyOne](./ibm-cloud-sdk-core.onlyone.md) ## onlyOne() function Checks that exactly one of the arguments provided is defined. Returns true if one argument is defined. Returns false if no argument are defined or if 2 or more are defined. **Signature:** ```typescript export declare function onlyOne(...args: any): boolean; ``` ## Parameters

Parameter	Type	Description
args	any	The spread of arguments to check

**Returns:** boolean true if and only if exactly one argument is defined