--- description: 'Disallow non-null assertions using the `!` postfix operator.' --- 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/no-non-null-assertion** for documentation. TypeScript's `!` non-null assertion operator asserts to the type system that an expression is non-nullable, as in not `null` or `undefined`. Using assertions to tell the type system new information is often a sign that code is not fully type-safe. It's generally better to structure program logic so that TypeScript understands when values may be nullable. ## Examples ```ts interface Example { property?: string; } declare const example: Example; const includesBaz = example.property!.includes('baz'); ``` ```ts interface Example { property?: string; } declare const example: Example; const includesBaz = example.property?.includes('baz') ?? false; ``` ## When Not To Use It If your project's types don't yet fully describe whether certain values may be nullable, such as if you're transitioning to `strictNullChecks`, this rule might create many false reports. You might consider using [ESLint disable comments](https://eslint.org/docs/latest/use/configure/rules#using-configuration-comments-1) for those specific situations instead of completely disabling this rule.