Preventing Undefined Values in RxJS Observables: A Guide

I am facing an issue with passing the result of a GET request from Observable to Observer. The problem lies in the fact that the value becomes undefined because it communicates with the observer before the GET execution finishes.

 observer:Observer<any> = {
  next: objectFromObservable => { SomeActionWith() }
}


let outputToObserver;
this.http.get(myUrl).map((programs)=>{
    const mapped = programs.json() as Program[];
    outputToObserver=mapped //here we always have desired object
    return mapped;
})
.subscribe(
(res)=>{
    return res; //here we always have desired object
}
)
//Here outputToObserver is undefined, so above lines are executed before mapping
let observable:Observable<any> = Observable.create(function (obserwator) {
observer.next(outputToObserver)

Answer №1

Here is an example of how you can achieve this

fetchDataFromMyEndpoint() {
  return this.http.get(myEndpoint).map((data)=>{
          const processed = data.json() as Data[];
          return processed;
      })
}

When using the data, follow these steps

var retrievedData = fetchDataFromMyEndpoint()
                .subscribe(response => {
                     // Perform operations on the data here....
                });

Answer №2

Utilizing the do method allows you to seamlessly trigger a side effect, enhancing readability and maintaining a linear code flow.

const outputChannel=new Subject()

this.http.get(targetUrl).map((data)=>data.json())
.do(result=>outputChannel.next(result))
.subscribe()

outputChannel.subscribe()

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