在Angular 9中点击上传文件前显示图片？

<input type="file" (change)="onFileSelected($event)">
<img *ngIf="imageUrl" [src]="imageUrl" alt="Selected Image">

imageUrl: string;

onFileSelected(event: any) {
  const file: File = event.target.files[0];
  const reader = new FileReader();

  reader.onload = (e: any) => {
    this.imageUrl = e.target.result;
  };

  reader.readAsDataURL(file);
}