Issue
I have an async function that calls multiple async calls in sequential order. However, it is returning undefined despite using the async and await keywords
Flow: currentPosition runs first then coordinates runs next then I can get the latitude and longitude of the coordinates
public async getAddressOfCurrentLocation () {
const currentPosition = await this.trackCurrentPosition()
const coordinates = await this.getCoordinates(currentPosition); // returns undefined, should return [lat, long in numerical format]
const latitude = await coordinates[0];
const longitude = await coordinates[1];
let options: NativeGeocoderOptions = {
useLocale: NATIVE_GEOCORDER_OPTIONS.USE_LOCALE,
maxResults: NATIVE_GEOCORDER_OPTIONS.MAX_RESULTS
};
const address = this.getAddressUsingCoordinates(latitude, longitude, options);
return address;
}
private async trackCurrentPosition() {
return await this.geolocationImplService.trackCurrentPosition()
}
private async getCoordinates(position: Observable<Geoposition | PositionError>) {
return await this.geolocationImplService.getCoordinates(position)
}
// ----------- geolocationImplService methods------------
public async trackCurrentPosition() {
return this.geolocation.watchPosition();
}
public async getCoordinates (position: Observable<Geoposition | PositionError>) {
position.subscribe( (positionData) => {
let result = [0,0]
if ("coords" in positionData) {
result[0] = positionData.coords.latitude;
result[1] = positionData.coords.longitude;
return result
}
return result
})
}
How do i solve this issue?
Solution
The return
is in a callback, not in the method itself. Therefore, you are not returning from the method (you are only returning from the callback). You can wrap the subscribe
call in a promise, and then return that promise like this:
public async getCoordinates (position: Observable<Geoposition | PositionError>) {
return new Promise((resolve) => {
position.subscribe((positionData) => {
let result = [0,0]
if ("coords" in positionData) {
result[0] = positionData.coords.latitude;
result[1] = positionData.coords.longitude;
return resolve(result);
}
return resolve(result);
});
});
}
Calling resolve
with the value you want the promise to resolve to. This is called "promisification" which you can read more about here.
Answered By - Kay
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