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docs(eslint-plugin): [no-explicit-any] add alternatives #11199

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30 changes: 30 additions & 0 deletions packages/eslint-plugin/docs/rules/no-explicit-any.mdx
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Expand Up @@ -145,6 +145,36 @@ interface Garply {
}
```

## Alternatives to `any`

Which type(s) to use instead of `any` depends on the context.

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I can't find references of other non-straightforward scenarios to add... are there others we should mention?

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@JoshuaKGoldberg JoshuaKGoldberg May 9, 2025 •
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TODO: Add more straightforward cases from earlier in the file...

  • If the type is known, describing it in an interface or type
    • Mention [i: string]/etc. index signatures too, either inside or alongside
  • If the type is not known, using the safer unknown type

### Type Parameter Constraints

"Generic" type parameters are often used to represent a value of an unknown type.
It can be tempting to use `any` as a type parameter constraint, but this is not recommended.

First, `extends any` on its own does nothing: `<T extends any>` is equivalent to `<T>`.
See [`@typescript-eslint/no-unnecessary-type-constraint`](./no-unnecessary-type-constraint.mdx) for more information.

Within type parameters, `never` and `unknown` otherwise can generally be used instead.
For example, the following code uses those two types in `AnyFunction` instead of `any`s to constrain `Callback` to any function type:

```ts
type AnyFunction = (...args: never[]) => unknown;

function curry<Greeter extends AnyFunction>(greeter: Greeter, prefix: string) {
return (...args: Parameters<Greeter>) => `${prefix}: ${greeter(...args)}`;
}

const greet = (name: string) => `Hello, ${name}!`;
const greetWithDate = curry(greet, 'Logged: ');

greetWithDate('linter'); // => "Logged: Hello, linter!"
```

See [When to use `never` and `unknown` in TypeScript](https://blog.logrocket.com/when-to-use-never-unknown-typescript) for more information on those types.

## When Not To Use It

`any` is always a dangerous escape hatch.
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