Angular data handler for async data calls.

Angular Data Handler

import { BehaviorSubject, Observable } from 'rxjs';

export class DataHandler<T> {
  value: T;
  value$: BehaviorSubject<T>;
  isLoading = false;
  hasError = false;
  error: any = null;
  errorIsString = false;
  successful = false;
  private defaultValue: T;

  constructor(defaultValue: T = null) {
    if (defaultValue) {
      this.defaultValue = defaultValue;
      this.value = defaultValue;
      this.successful = true;
    }
    this.value$ = new BehaviorSubject<T>(defaultValue);
  }

  async request(response: Observable<T>): Promise<T> {
    this.isLoading = true;
    this.hasError = false;
    this.error = null;
    this.successful = false;
    this.errorIsString = false;
    try {
      const result = await response.toPromise();
      this.value$.next(result);
      this.value = result;
      this.successful = true;
      return result;
    } catch (err) {
      if (typeof err.error === 'string') {
        try {
          this.error = JSON.parse(err.error);
        } catch (error) {
          this.error = err.error;
          this.errorIsString = true;
        }
      } else {
        this.error = err.error;
      }
      this.hasError = true;
    } finally {
      this.isLoading = false;
    }
  }

  setErrorState(error: string) {
    this.reset();
    this.hasError = true;
    this.error = error;
    this.errorIsString = true;
  }

  reset() {
    this.value = null;
    this.isLoading = false;
    this.hasError = false;
    this.error = null;
    this.value$ = new BehaviorSubject<T>(this.defaultValue);
  }
}