--- description: 'Enforce non-null assertions over explicit type assertions.' --- import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem'; > 🛑 This file is source code, not the primary documentation location! 🛑 > > See **https://typescript-eslint.io/rules/non-nullable-type-assertion-style** for documentation. There are two common ways to assert to TypeScript that a value is its type without `null` or `undefined`: - `!`: Non-null assertion - `as`: Traditional type assertion with a coincidentally equivalent type `!` non-null assertions are generally preferred for requiring less code and being harder to fall out of sync as types change. This rule reports when an `as` assertion is doing the same job as a `!` would, and suggests fixing the code to be an `!`. ## Examples ```ts const maybe: string | undefined = Math.random() > 0.5 ? '' : undefined; const definitely = maybe as string; const alsoDefinitely = maybe; ``` ```ts const maybe: string | undefined = Math.random() > 0.5 ? '' : undefined; const definitely = maybe!; const alsoDefinitely = maybe!; ``` ## When Not To Use It If you don't mind having unnecessarily verbose type assertions, you can avoid this rule.