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71 lines
1.8 KiB
Text
71 lines
1.8 KiB
Text
---
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description: 'Disallow non-null assertions after an optional chain expression.'
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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-optional-chain** for documentation.
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## Rule Details
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Optional chain expressions are designed to return `undefined` if the optional property is nullish.
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Using non-null assertions after an optional chain expression is wrong, and introduces a serious type safety hole into your code.
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Examples of code for this rule:
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<!--tabs-->
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### ❌ Incorrect
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```ts
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/* eslint @typescript-eslint/no-non-null-asserted-optional-chain: "error" */
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foo?.bar!;
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foo?.bar()!;
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// Prior to TS3.9, foo?.bar!.baz meant (foo?.bar).baz - i.e. the non-null assertion is applied to the entire chain so far.
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// For TS3.9 and greater, the non-null assertion is only applied to the property itself, so it's safe.
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// The following is incorrect code if you're using less than TS3.9
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foo?.bar!.baz;
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foo?.bar!();
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foo?.bar!().baz;
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```
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### ✅ Correct
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```ts
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/* eslint @typescript-eslint/no-non-null-asserted-optional-chain: "error" */
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foo?.bar;
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(foo?.bar).baz;
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foo?.bar();
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foo?.bar();
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foo?.bar().baz;
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// The following is correct code if you're using TS3.9 or greater
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foo?.bar!.baz;
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foo?.bar!();
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foo?.bar!().baz;
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```
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## Options
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```jsonc
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// .eslintrc.json
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{
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"rules": {
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"@typescript-eslint/no-non-null-asserted-optional-chain": "error"
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}
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}
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```
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This rule is not configurable.
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## When Not To Use It
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If you are not using TypeScript 3.7 (or greater), then you will not need to use this rule, as the operator is not supported.
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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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- [Optional Chaining Proposal](https://github.com/tc39/proposal-optional-chaining/)
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