angular upload reactive form

@Component({
  template: `
    <form [formGroup]="formGroup" novalidate (ngSubmit)="onSubmit()">
      <input type="file" (change)="onFileChange($event)" />
      <button type="submit" [disabled]="formGroup.invalid || formGroup.prestine">Submit</button>
    </form>
  `
})
export class PizzaComponent {

  formGroup = this.fb.group({
    file: [null, Validators.required]
  });

  constructor(private fb: FormBuilder, private cd: ChangeDetectorRef) {}

  onFileChange(event) {
    const reader = new FileReader();

    if(event.target.files && event.target.files.length) {
      const [file] = event.target.files;
      reader.readAsDataURL(file);

      reader.onload = () => {
        this.formGroup.patchValue({
          file: reader.result
       });

        // need to run CD since file load runs outside of zone
        this.cd.markForCheck();
      };
    }
  }

}