49 lines
1.5 KiB
Plaintext
49 lines
1.5 KiB
Plaintext
---
|
|
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
|
|
|
|
<Tabs>
|
|
<TabItem value="❌ Incorrect">
|
|
|
|
```ts
|
|
interface Example {
|
|
property?: string;
|
|
}
|
|
|
|
declare const example: Example;
|
|
const includesBaz = example.property!.includes('baz');
|
|
```
|
|
|
|
</TabItem>
|
|
<TabItem value="✅ Correct">
|
|
|
|
```ts
|
|
interface Example {
|
|
property?: string;
|
|
}
|
|
|
|
declare const example: Example;
|
|
const includesBaz = example.property?.includes('baz') ?? false;
|
|
```
|
|
|
|
</TabItem>
|
|
</Tabs>
|
|
|
|
## 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.
|