---
url: /docs/guide/usage/linter/rules/typescript/no-non-null-assertion.md
---

### What it does

Disallow non-null assertions using the `!` postfix operator.

### Why is this bad?

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

Examples of **incorrect** code for this rule:

```ts
x!;
x!.y;
x.y!;
```

Examples of **correct** code for this rule:

```ts
x;
x?.y;
x.y;
```

## How to use

## Version

This rule was added in v0.5.0.

## References