Angular 2: Issue with Observable subscription not correctly retrieving data

When attempting to retrieve an array of objects from the ngrx Store and assign it to an array using the subscribe option provided by Observables in Angular 2, an issue arises when trying to access the contents of the array. Below is a snippet of the code:

 metaData$: Observable<MetaClassDefinition[]>;
    myArray: MetaClassDefinition[] = [];  

    constructor(private store: Store<fromRoot.State>) {
      this.metaData$ = store.select(fromRoot.getMetadata);
    }

    this.metaData$.subscribe(
       data => {
          if (data.length > 0) {
             // Deep copy array
             data.forEach(v => this.myArray.push({...v}));
          }
       },
       error => { console.log(error)}
    );

    console.log(this.myArray);  //-------(1)
    console.log(this.myArray.length);   //-------(2)

When the 1st console.log is executed, the array of objects is printed like this:

https://i.sstatic.net/bEpBz.png

However, when attempting to print the 2nd console.log, the size of the array is shown as zero. Is there something missing from this code that I am overlooking?

Answer №1

The reason for this behavior is the timing discrepancies associated with asynchronous operations. Try moving the console statements inside the subscribe function to gain a clearer understanding of the expected results.

In addition, by logging the object reference in the console and then checking it later, you can confirm that the data has been successfully retrieved and is visible in the debugger.

It is important to note that the array count is calculated immediately (before the data is fetched), and since it is a static number, it does not get re-calculated.

Answer №2

You should consider printing the array information inside the subscribe function.

this.metaData$.subscribe(
       data => {
          if (data.length > 0) {
             // Make a deep copy of the array
             data.forEach(v => this.myArray.push({...v}));
             //TODO: Print array information
             console.log(this.myArray);  //-------(1)
             console.log(this.myArray.length);   //-------(2)
            // Done printing array information  
          }
       },
       error => { console.log(error)}
    );

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