Flag to type `Promise.catch` variables as `unknown`

Suggestion

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn’t be a breaking change in existing TypeScript/JavaScript code
• This wouldn’t change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn’t a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript’s Design Goals.

⭐ Suggestion

Following #41016 a flag was added to consider catch variables as unknown. For consistency and since they’re similar cases, I suggest also adding a flag that does this for .catch callbacks on promises.

See also: eslint-plugin-etc/no-implicit-any-catch

[Cellule]

You can easily achieve this by overloading the signature of Promise.catch in your project

// Promise.d.ts
interface Promise<T> {
  /**
   * Attaches a callback for only the rejection of the Promise.
   * @param onrejected The callback to execute when the Promise is rejected.
   * @returns A Promise for the completion of the callback.
   */
  catch<TResult = never>(
    onrejected?: ((reason: unknown) => TResult | PromiseLike<TResult>) | undefined | null,
  ): Promise<T | TResult>;
}

[yoav-lavi]

@Cellule Thanks for the snippet, yes, you can do this yourself, but the goal of this suggestion is to add this to TS itself