typescript callback type mismatch

Question

I have this code in callback many places :

return new Promise<Result> (
        (resolve : (Result ) =>void,reject: ( any) =>void) =>{
    .......
   });

I thought I will create an interface for this long type :

interface callback<T> {
   resolve : (value? :T ) =>void;
    reject  : (error? : any) =>void;  
}

But I cannot use it in place like :

return new Promise<Result> ( 
( c : Callback<Result> ) = > {
 ......
}

TS complains that Callback is not a resolve: Result => void.

How can I make it work?

Vadim Macagon · Accepted Answer · 2016-02-05 04:35:03Z

1

Promises are already typed if you're targeting ES6, there are typings for shims if you target ES5, and typings for non-native Promise libs. So, you shouldn't need to write your own type definition for this. When constructing a promise this is the only code you need to write:

new Promise<TypeOfResult>((resolve, reject) => {
  // do yar thing
})

TypeScript will infer the type of resolve and reject so specifying their type explicitly is redundant and needlessly verbose.

answered Feb 5, 2016 at 4:35

Vadim Macagon

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