我想在我的代碼上實現這個過濾，但我在實現它時遇到了問題。我在實現這行代碼時出錯：function search(text: string, pipe: PipeTransform): Country[] {  return COUNTRIES.filter(country => {    const term = text.toLowerCase();    return country.name.toLowerCase().includes(term)        || pipe.transform(country.area).includes(term)        || pipe.transform(country.population).includes(term);  });}我無法更改COUNTRIES.filter，當我嘗試在其上放置/替換我的函數時出現錯誤。我收到此錯誤“ 'void'類型上不存在屬性'過濾器' ”這是我的代碼。export class MyComponent implements OnInit {  countries: Observable<any[]>;  filter = new FormControl('');  listQuestions = [];  constructor(private extractorService: ExtractorService,               private fstore: AngularFirestore) { }  ngOnInit() {   this.filterFunction();  }  filterFunction(){    this.countries = this.filter.valueChanges.pipe(      startWith(''),      map(text => this.search(text))    );  }  search(text: string): any[] {    return this.sampleFunction().filter(country => {      const term = text.toLowerCase();        return country.caseID.toLowerCase().includes(term)            || (country.word).toLowerCase().includes(term)            || (country.product).toLowerCase().includes(term);    });  }  sampleFunction() {    this.extractorService.dbFirestore().subscribe(data => {      this.listQuestions = data.map(x => {        return x.payload.doc.data();      })    })  }我可以從我的sampleFunction()獲取來自 firebase 的所有數據。順便說一句，我使用以下代碼在 html 上加載數據：<tr *ngFor="let item of countries | async">您能幫我將我在sampleFunction()上獲得的數據用于指南使用“ return COUNTRIES.filter(country => {”行的搜索功能嗎