rxjs-file-reader.ts

rxjs-file-reader.ts

import { Observable, Subscriber } from 'rxjs';

function readAs(
  blob: Blob,
  as: 'ArrayBuffer' | 'BinaryString' | 'DataURL' | 'Text',
  encoding?: string
): Observable<any> {
  return new Observable(
    (subscriber: Subscriber<string | ArrayBuffer | null>) => {
      const fileReader = new FileReader();

      fileReader.onload = (ev) => {
        subscriber.next((ev.target as FileReader).result);
        subscriber.complete();
      };
      fileReader.onerror = (error): void => {
        subscriber.error(error);
      };

      fileReader[`readAs${as}`](blob, encoding);

      return () => {
        fileReader.abort();
      };
    }
  );
}

export function readAsArrayBuffer(blob: Blob): Observable<ArrayBuffer> {
  return readAs(blob, 'ArrayBuffer');
}

export function readAsBinaryString(blob: Blob): Observable<string> {
  return readAs(blob, 'BinaryString');
}

export function readAsDataURL(blob: Blob): Observable<string> {
  return readAs(blob, 'DataURL');
}

export function readAsText(blob: Blob, encoding?: string): Observable<string> {
  return readAs(blob, 'Text', encoding);
}