97 lines
2.9 KiB
Plaintext
97 lines
2.9 KiB
Plaintext
---
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description: 'Disallow assigning a value with type `any` to variables and properties.'
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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-unsafe-assignment** for documentation.
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The `any` type in TypeScript is a dangerous "escape hatch" from the type system.
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Using `any` disables many type checking rules and is generally best used only as a last resort or when prototyping code.
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Despite your best intentions, the `any` type can sometimes leak into your codebase.
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Assigning an `any` typed value to a variable can be hard to pick up on, particularly if it leaks in from an external library.
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This rule disallows assigning `any` to a variable, and assigning `any[]` to an array destructuring.
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This rule also compares generic type argument types to ensure you don't pass an unsafe `any` in a generic position to a receiver that's expecting a specific type.
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For example, it will error if you assign `Set<any>` to a variable declared as `Set<string>`.
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## Examples
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<!--tabs-->
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### ❌ Incorrect
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```ts
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const x = 1 as any,
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y = 1 as any;
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const [x] = 1 as any;
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const [x] = [] as any[];
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const [x] = [1 as any];
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[x] = [1] as [any];
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function foo(a = 1 as any) {}
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class Foo {
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constructor(private a = 1 as any) {}
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}
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class Foo {
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private a = 1 as any;
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}
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// generic position examples
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const x: Set<string> = new Set<any>();
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const x: Map<string, string> = new Map<string, any>();
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const x: Set<string[]> = new Set<any[]>();
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const x: Set<Set<Set<string>>> = new Set<Set<Set<any>>>();
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```
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### ✅ Correct
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```ts
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const x = 1,
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y = 1;
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const [x] = [1];
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[x] = [1] as [number];
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function foo(a = 1) {}
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class Foo {
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constructor(private a = 1) {}
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}
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class Foo {
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private a = 1;
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}
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// generic position examples
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const x: Set<string> = new Set<string>();
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const x: Map<string, string> = new Map<string, string>();
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const x: Set<string[]> = new Set<string[]>();
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const x: Set<Set<Set<string>>> = new Set<Set<Set<string>>>();
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```
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<!--/tabs-->
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There are cases where the rule allows assignment of `any` to `unknown`.
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Example of `any` to `unknown` assignment that are allowed:
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```ts showPlaygroundButton
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const x: unknown = y as any;
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const x: unknown[] = y as any[];
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const x: Set<unknown> = y as Set<any>;
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```
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## When Not To Use It
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If your codebase has many existing `any`s or areas of unsafe code, it may be difficult to enable this rule.
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It may be easier to skip the `no-unsafe-*` rules pending increasing type safety in unsafe areas of your project.
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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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## Related To
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- [`no-explicit-any`](./no-explicit-any.md)
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- [`no-unsafe-argument`](./no-unsafe-argument.md)
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- [`no-unsafe-call`](./no-unsafe-call.md)
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- [`no-unsafe-member-access`](./no-unsafe-member-access.md)
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- [`no-unsafe-return`](./no-unsafe-return.md)
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