如何在javascript中的异步等待中返回承诺？

Question

Is it ok to do something like this?

I mean, Is return await new Promise() a valid expression as of below?:

  async pushImage(image, basePath) {
    const imgId = this.angularDatabase.createPushId();
    const route = `${basePath}${imgId}`;
    const imageRef = this.angularFireStorage.ref(route);
    
    return await concat( 
      imageRef.put(image.image).snapshotChanges().pipe(ignoreElements()),
      defer(() => imageRef.getDownloadURL())
    )
      .pipe(
        map(
          (url) => (
             { ...image, url }
          )
        )
      )
      .toPromise();
  }

Answer 1

Anything returned from an async functions comes out as a promise.

For example:

async getDate() {
   return new Date();
}

will return a promise with the contents of a date.

An example of reading this overly complicated getDate() function would be:

getDate().then(date => {
   console.log("The date: ", date);
});

However, you can also return a promise. This makes your code above perfectly valid, except you don't need to include the await in the return.

You can "simply" just say

return concat( 
          imageRef.put(image.image).snapshotChanges().pipe(ignoreElements()),
          defer(() => imageRef.getDownloadURL())
       ).pipe(
          map(url => {
             return {...image, url}
          })
       ).toPromise();

Side note: I am not certain, but I think you should return the object in the map. Changing {...image, url} to return {...image, url}

Additional response:

To retrieve the contents of a promise, use the .then() method. Example:

myReturnedPromise.then(dataOfMyReturnedPromise => {
   //This code is called after the promise is resolved.
   console.log("The returned value is: ", dataOfMyReturnedPromise);
}).catch(error => {
   //If this code is called, the promise completed with an error
   //This might be executed if you're retreiving data from the internet
   //and your internet connection is too poor to get the data
   console.error("Error: ", error);
});

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