Resolved value from promise is always {} from compile time, cause error

[alanpurple]

it seems that type checking always fails except type 'any; for resolved value from Promise

public data:SomeType

getData(){
this._someService.getData().then(data=>this.data=data); // always emit TS2332 error
}

with
public data;

it works

[vladima]

cannot repro locally using the latest bits on master:

interface SomeType { x }
interface Service { getData(): Promise<SomeType> }
class A {
    _someService: Service;
    data: SomeType;
    getData(){
        this._someService.getData().then(data=>this.data=data);
    }
}

node built\local\tsc.js D:\sources\bugs\a.ts -t es6 yields no errors and produces the following javascript:

class A {
    getData() {
        this._someService.getData().then(data => this.data = data);
    }
}

Can you check if your scenario has any specifics that reveal the problem?

[alanpurple]

@vladima

official angular2 site tutorial

https://angular.io/docs/ts/latest/tutorial/toh-pt4.html

export class AppComponent implements OnInit {
  public title = 'Tour of Heroes';
  public heroes: Hero[];
  public selectedHero: Hero;
  constructor(private _heroService: HeroService) { }
  getHeroes() {
    this._heroService.getHeroes().then(heroes => this.heroes = heroes);
  }
  ngOnInit() {
    this.getHeroes();
  }
  onSelect(hero: Hero) { this.selectedHero = hero; }
}

TS2332: length property missing, {} cannot be assigned to type Hero[]

[vladima]

still cannot repro. I've downloaded the sample from this link, added tsconfig.json and tried to build the code - still cannot see any errors. My repro bits can be found here, can you check if there are any differences in your code?

[alanpurple]

@vladima If my code is wrong, without ':Hero[]' there should be an error also

and even before compiling, there's already an red underscore error mark from intellisense

my environment is Windows 10 x64 + VS2015 + TypeScript 1.7.5

[alanpurple]

tsconfig - same as angular.io quickstart guide

car.ts

export interface Car {
    id: number,
    name: string
}

car.service.ts

import {Injectable} from 'angular2/core';
import {Car} from './car';
import {CARS} from './mock-cars';

@Injectable()
export class CarService {
    getCars() {
        return new Promise(resolve=>
            setTimeout(() => resolve(CARS), 2000)
        );
    }
}

mock.cars.ts

import {Car} from './car';

export var CARS: Car[] = [
    { id: 1, name: 'BMW M4' },
    { id: 2, name: 'Audi A8' },
    { id: 3, name: 'LandRover Range Rover Sport' }
];

[DanielRosenwasser]

Quick tip @alanpurple - I've been fixing your examples, but you should surround your code samples with code fences.

Start your code off with ````ts` and end it with `````.

[alanpurple]

@DanielRosenwasser Yeah thanks for the tip :)

[DanielRosenwasser]

I think the problem is that there's nothing we can infer for the type argument in getCars. If you make your getCars the following:

    getCars() {
        // Notice the type argument 'Car[]'
        return new Promise<Car[]>(resolve=>
            setTimeout(() => resolve(CARS), 2000)
        );
    }

I think that should take care of it.

#5254 is probably related.

[alanpurple]

@DanielRosenwasser Thx, solved, and sorry for not seeing correctly

[DanielRosenwasser]

No problemo! It can be pretty subtle.