Promise rejection type.

Search Terms

Promise Reject Type

Suggestion

Add ability to type Promise rejections.

// Current Promise Constructor Implementation:
new <T>(executor: (resolve: (value?: T | PromiseLike<T>) => void, reject: (reason?: any) => void) => void): Promise<T>;

// Proposed Change:
new <T, E = any>(executor: (resolve: (value?: T | PromiseLike<T>) => void, reject: (reason?: E) => void) => void): Promise<T, E>;

Use Cases

When handling promise rejections, the type any isn't very useful. I would be useful to have the rejection have an actual type without the need to cast or type guard.

Examples

Promise.reject<never, string>('hello world')
  .catch(reason => {
    console.error(reason.length); // `reason` is of type string.
  });

class MyError extends Error {
  // ...
}

Promise.reject<never, MyError>(new MyError(/* ... */))
  .catch(reason => {
    // `reason` is of type MyError.
    const info = reason.getMoreInfo();
    // ...
  });

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, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Commencez par les exemples de Promise constructor et Promise.reject dans l’issue, puis examinez la discussion environnante à la recherche de contraintes de conception et d’objections non résolues. Le travail ne sera terminé que lorsque l’équipe se sera accordée sur une conception du type de rejet et sur son comportement lors de la construction, du rejet et de la gestion de catch.