55 lines
1.6 KiB
Plaintext
55 lines
1.6 KiB
Plaintext
---
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description: 'Disallow non-null assertions in the left operand of a nullish coalescing operator.'
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---
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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/no-non-null-asserted-nullish-coalescing** for documentation.
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The `??` nullish coalescing runtime operator allows providing a default value when dealing with `null` or `undefined`.
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Using a `!` non-null assertion type operator in the left operand of a nullish coalescing operator is redundant, and likely a sign of programmer error or confusion over the two operators.
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## Examples
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<!--tabs-->
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### ❌ Incorrect
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```ts
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foo! ?? bar;
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foo.bazz! ?? bar;
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foo!.bazz! ?? bar;
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foo()! ?? bar;
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let x!: string;
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x! ?? '';
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let x: string;
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x = foo();
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x! ?? '';
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```
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### ✅ Correct
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```ts
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foo ?? bar;
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foo ?? bar!;
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foo!.bazz ?? bar;
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foo!.bazz ?? bar!;
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foo() ?? bar;
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// This is considered correct code because there's no way for the user to satisfy it.
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let x: string;
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x! ?? '';
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```
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## When Not To Use It
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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.
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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.
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## Further Reading
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- [TypeScript 3.7 Release Notes](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html)
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- [Nullish Coalescing Proposal](https://github.com/tc39/proposal-nullish-coalescing)
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