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Incorrect return types for Promise#catch and 0- and 2- arg forms of Promise#then #9193
Description
| Expression (p: Promise) | Correct type | Current type |
|---|---|---|
| p.then() | Promise | Promise<{}> |
| p.then(b => 1) | Promise | Promise |
| p.then(b => 1, e => 'error') | Promise<number | string> |
| p.then(b => 1, e => {}) | Promise<number | void> |
| p.then(b => 1, e => {throw Error()}) | Promise | Promise |
| p.then(b => 1, e => Promise.reject(Error())) | Promise | Promise |
| p.catch(e => 'error') | Promise<boolean | string> |
| p.catch(e => {}) | Promise<boolean | void> |
| p.catch(e => {throw Error()}) | Promise | Promise |
| p.catch(e => Promise.reject(Error())) | Promise | Promise |
Using overloading and the new never type, PromiseLike/Promise could be typed to handle all these cases correctly:
interface PromiseLike<T> {
then(): PromiseLike<T>;
then<R1>(onfulfilled: (value: T) => R1 | PromiseLike<R1>): PromiseLike<R1>;
then<R1, R2>(onfulfilled: (value: T) => R1 | PromiseLike<R1>,
onrejected: (reason: any) => R2 | PromiseLike<R2>): PromiseLike<R1 | R2>;
}
interface Promise<T> {
then(): Promise<T>;
then<R1>(onfulfilled: (value: T) => R1 | PromiseLike<R1>): Promise<R1>;
then<R1, R2>(onfulfilled: (value: T) => R1 | PromiseLike<R1>,
onrejected: (reason: any) => R2 | PromiseLike<R2>): Promise<R1 | R2>;
catch<R2>(onrejected: (reason: any) => R2 | PromiseLike<R2>): Promise<T | R2>;
}
declare var Promise: {
reject(reason: any): Promise<never>; // Returned promise is never fulfilled
};
Activity
mhegazy commentedon Jun 15, 2016
//cc: Ron Buckton (@rbuckton)
rbuckton commentedon Jun 15, 2016
There are a few things we need to fix in the checker for properly handling
neverin these cases with async functions, and there's a breaking change in the definition forPromiseLikeandPromisethat needs to be resolved, but this seems like the right direction.Updates type definitions for Promise and PromiseLike, fixes issues in…