[getImageURL] Observable #firebase

firebase_get_url.ts

imageObservables = {};

  getImageUrl(ref: string) {
    if (!ref) { return; }
    const regEx: RegExp = /^[0-9]/;
    if (!regEx.test(ref.charAt(0))) { return; }

    if (ref in this.imageObservables) {
      return this.imageObservables[ref];
    } else {
      this.imageObservables[ref] = this.storageService.getMenuPicUrl(ref);
      return this.imageObservables[ref];
    }
  }

/* ...html
<img [src]="getImageUrl('fileName.png') | async">
<img src="{(getImageUrl('fileName.png') | async)}">
  */