可观的承诺迫不及待地实现

Question

I have written a function that will get the IMDB ratings of an IMDB ID through an API. This is the function to which i pass the IMDB ID

async function movieDetails(ID){
    let ratings= await getDetails(ID);
    return ratings;
}

And this is the function that returns the IMDB ratings.

const getDetails = val =>{
    return Rx.Observable.fromPromise(fetch(`http://www.omdbapi.com/?i=${val}&plot=full&apikey=${APIKey}`)
    .then(e => e.json())
    .catch(err => console.log(err)))
    .map(e => e.imdbRating)
    .subscribe(x => {
        console.log(x);
        return x;
    }, e => console.error(e));
}

But this function is returning a promise object instead of IMDB rating. And this is the output which i get on the console.

Promise {[[PromiseStatus]]: "pending", [[PromiseValue]]: undefined}

Promise {[[PromiseStatus]]: "pending", [[PromiseValue]]: undefined}

8.1

7.3

8.1 and 7.3 are the values from the console statement in getDeatils() which is what i am returning. And the promise object are printed when movieDetails() is called. Can anyonebody point me out, what i am doing wrong here ?

Answer 1

getDetails function returns subscription , and in movieDetails you are await ing those subscription. In short, it doesn't work.

When you subscribe into created observable you get subscription to control its lifecycle. Those subscription doesn't do anything with values of observables.

const obs = Observable.from(...) //obs is Observable
const subs = obs.subscribe((x) => console.log(x)); //subs is Subscription

// subs.unsubscribe(); //when you want to unsubscribe even source does not completes

Secondly, you can't directly await Observables - await keyword is for Promise. In Observables, observer is way to access values (function supplied in subscribe ). If you should use await, convert Observables into toPromise and get only latest number - otherwise, just return observable in getDetail then access values via observer is way to go.