fix(storage): use backward compatible return type in download function (#1750)

Author: itslenny

packages/core/storage-js/src/packages/BlobDownloadBuilder.ts

@@ -2,7 +2,10 @@ import { isStorageError } from '../lib/errors'
 import { DownloadResult } from '../lib/types'
 import StreamDownloadBuilder from './StreamDownloadBuilder'
 
-export default class BlobDownloadBuilder implements PromiseLike<DownloadResult<Blob>> {
+export default class BlobDownloadBuilder implements Promise<DownloadResult<Blob>> {
+  readonly [Symbol.toStringTag]: string = 'BlobDownloadBuilder'
+  private promise: Promise<DownloadResult<Blob>> | null = null
+
   constructor(
     private downloadFn: () => Promise<Response>,
     private shouldThrowOnError: boolean
@@ -16,7 +19,24 @@ export default class BlobDownloadBuilder implements PromiseLike<DownloadResult<B
     onfulfilled?: ((value: DownloadResult<Blob>) => TResult1 | PromiseLike<TResult1>) | null,
     onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | null
   ): Promise<TResult1 | TResult2> {
-    return this.execute().then(onfulfilled, onrejected)
+    return this.getPromise().then(onfulfilled, onrejected)
+  }
+
+  catch<TResult = never>(
+    onrejected?: ((reason: any) => TResult | PromiseLike<TResult>) | null
+  ): Promise<DownloadResult<Blob> | TResult> {
+    return this.getPromise().catch(onrejected)
+  }
+
+  finally(onfinally?: (() => void) | null): Promise<DownloadResult<Blob>> {
+    return this.getPromise().finally(onfinally)
+  }
+
+  private getPromise(): Promise<DownloadResult<Blob>> {
+    if (!this.promise) {
+      this.promise = this.execute()
+    }
+    return this.promise
   }
 
   private async execute(): Promise<DownloadResult<Blob>> {