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