[Home](./index.md) > [rc-js-util](./rc-js-util.md) > [\_Production](./rc-js-util._production.md) > [assertValueIsNever](./rc-js-util._production.assertvalueisnever.md) ## \_Production.assertValueIsNever() method A function that will error if ever called. The parameter is asserted to be never, useful with switch statements, union types etc. **Signature:** ```typescript static assertValueIsNever(_value: never): never; ``` ## Parameters

Parameter	Type	Description
\_value	never

**Returns:** never ## Example ```typescript // adding extra values to the enum will cause a compiler error enum ETest { Foo = 1 }; function test(value: ETest) { switch (value) { case ETest.Foo: return "potato"; default: return _Production.assertValueIsNever(value); } } ```