How to access a variable from outside a promise block in Angular

Question

How to access a variable from outside a promise block in Angular

Is there a way to access a variable declared outside of a promise block within an Angular 6 component?

Consider the following scenario:


items: string[] = [];

ngOnInit() {

    const url='SOME URL';
    const promise = this.apiService.post(url);

    // Response
    promise.then(response => {
        this.items.push('abc');
        this.items.push('def');
    });

    this.items.forEach(item => {
        alert(item);
    });

}

I anticipate that the application will display alerts containing the contents of the items array.

angular typescript promise angular6

Answer 1

Answer №1

When you run the code snippet:

this.items.forEach(item=>{
     alert(item);
    });

you will find that the items array is empty initially.

To populate the items array before running the forEach loop, you should place the code inside a promise like this:

  promise.then(response => {
          this.items.push('abc');
          this.items.push('def');
         this.items.forEach(item=>{
            alert(item);
           });
     });

If you prefer using Observables instead of promises to ensure the items are loaded before executing the forEach loop, you can modify the code as follows:

private subjectItems = new Subject<any>();

ngOnInit{

    this.subjectItems.asObservable().subscribe(o => {
        this.items.forEach(item=>{
         alert(item);
        });
      });

    const url='SOME URL';
    const promise = this.apiService.post(url);

        //Response
        promise.then(response => {
           this.items.push('abc');
           this.items.push('def');

           this.subjectItems.next(this.items)
        });
      }

Answer 2

When you run the code snippet:

this.items.forEach(item=>{
     alert(item);
    });

you will find that the items array is empty initially.

To populate the items array before running the forEach loop, you should place the code inside a promise like this:

  promise.then(response => {
          this.items.push('abc');
          this.items.push('def');
         this.items.forEach(item=>{
            alert(item);
           });
     });

If you prefer using Observables instead of promises to ensure the items are loaded before executing the forEach loop, you can modify the code as follows:

private subjectItems = new Subject<any>();

ngOnInit{

    this.subjectItems.asObservable().subscribe(o => {
        this.items.forEach(item=>{
         alert(item);
        });
      });

    const url='SOME URL';
    const promise = this.apiService.post(url);

        //Response
        promise.then(response => {
           this.items.push('abc');
           this.items.push('def');

           this.subjectItems.next(this.items)
        });
      }

Answer 3

Answer №2

There appears to be an asynchronous problem at hand here. Your alert is being displayed before the data is retrieved from the service. One approach could be to utilize Observables and subscribe, ensuring that it waits for the data to be fetched before proceeding.

You may also consider employing async/await as detailed in this article

Answer 4

There appears to be an asynchronous problem at hand here. Your alert is being displayed before the data is retrieved from the service. One approach could be to utilize Observables and subscribe, ensuring that it waits for the data to be fetched before proceeding.

You may also consider employing async/await as detailed in this article

How to access a variable from outside a promise block in Angular

Answer №1

Answer №2

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