Ensuring efficient synchronization in Angular: Waiting for completion of two calls

I am facing an issue with a function that I need to run. The problem is that it does not wait for both calls to finish and instantiate rule1 and rule2, leading to an error stating that rule1.optionhead is undefined. I attempted nesting the code within each subscribe but then the execution occurs more times than intended. How can I resolve this?

In order to provide clarity, I am using this for loop as the selectedScenario contains an array of IDs which are part of an input form using ngValue

saveFunction() {

  for (const pair of this.selectedScenario) {
    this.ruleToSave = null;

    this.ruleService.find(pair[0]).subscribe((ruleResponse: HttpResponse < Rule > ) => {
      this.rule1 = ruleResponse.body;

    });

    this.ruleService.find(pair[1]).subscribe((ruleResponse: HttpResponse < Rule > ) => {
      this.rule2 = ruleResponse.body;

    });

    const head1 = this.rule1.optionHead;
    const head2 = this.rule2.optionHead;

    if (
      this.selectedOption === head1 &&
      this.selectedOption !== head2 &&
      (this.selectedWeakerOption === '' || head2 === this.selectedWeakerOption)
    ) {
      ..some code
      this.subscribeToSaveResponse(this.ruleService.createRule(this.ruleToSave));
    }

  }
}

Answer №1

Consider Using ForkJoin Technique

  By employing the Observable.forkJoin method, you can simultaneously fetch data from two different API calls and subscribe to the combined result as shown below:
  
                Observable.forkJoin([
                this.ruleService.find(pair[0]),
                this.ruleService.find(pair[1])])
                .subscribe(
    (result: any[]) =>{ 
           this.rule1 = result[0]; 
           this.rule1 = result[1]; 

        // Your additional code goes here

    }
    );

Answer №2

Here is the recommended code snippet to achieve that:

clearStorage() {
  Promise.all([
    this.storage.remove(item1),
    this.storage.remove(item2),
    this.storage.remove(item3),
  ]).then(result => performAction());

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