Trying to enter the function, but it exits without executing

I'm facing an issue with my function that involves making multiple calls to an observer. I need the function to wait until all the calls are complete before returning. I attempted putting the return statement inside the subscribe method, but it resulted in an error because the function's type is void without the return being the last thing.

 CheckIfReady(){
    var isReady;
    this.Room.subscribe(snapshot => {
      if(snapshot.Ready == "true"){ 
         console.log("Ready");
         isReady = true;
      }else{
        console.log("Not Ready");
        isReady = false;
      }
  });
  console.log('Is the Room Ready?', isReady); //undefined
  return isReady;  //returns undefined
}

Answer №1

To transform the observable into a promise, utilize toPromise. The consumer can then chain a then method:

isRoomReady(){
    return this.Room.toPromise().then(snapshot => snapshot.Ready === "true");
}

// Consumer
this.isRoomReady().then(status => console.log("Room is ready:", status));

It is assumed that the observable only emits a single snapshot value.

Answer №2

It seems like the Room object is using observables from RxJS. Observables are data streams that operate asynchronously. To handle this asynchronous behavior, you'll need to use a method that supports awaiting async code.

There are several ways to accomplish this:

Using Callbacks

class X {

    room: any; // Is Room an "observable"?

    readyQ(cb) {
        this.room.subscribe(snapshot => {
            if(snapshot.Ready == "true"){ 
                cb(true);
            } else {
                cb(false);
            }
        });
    }

    doSomething() {
        this.readyQ((isReady) => {
            if (isReady) {
                // ... perform some action
            }
        });
    }
}

Using Promises

class X {

    room: any; // Is Room an "observable"?

    readyQ(){
        return new Promise((resolve, reject) => {
            this.room.subscribe(snapshot => {
                if(snapshot.Ready == "true"){ 
                    resolve(true);
                } else {
                    resolve(false);
                }
            });
        });
    }

    doSomething() {
        this.readyQ().then((isReady) => {
            if (isReady) {
                // ... perform some action
            }
        });
    }
}

Using Async / Await

class X {

    room: any; // Is Room an "observable"?

    readyQ() {
        return new Promise((resolve, reject) => {
            this.room.subscribe(snapshot => {
                if(snapshot.Ready == "true"){ 
                    resolve(true);
                } else {
                    resolve(false);
                }
            });
        });
    }

    async doSomething() {
        var isReady = await this.readyQ();
        if (isReady) {
            // ... perform some action
        }
    }
}

Async / Await closely resembles synchronous code execution and may suit your needs better in handling observable data streams.

Answer №3

Given that Room operates as an asynchronous observable, wrapping the subscription in a promise may not offer significant benefits unless you intend to modify its output:

retrieveData(): Promise<any> {
    let response = new Promise<any>((resolve, reject) => {
        this.Room.subscribe(snapshot => resolve(snapshot), error => reject(error));
    }
    return response;
}

retrieveData().then(response => {
    // implement your code here
}).catch(error => console.error(error));

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