undefined is not iterable (cannot read property Symbol(Symbol.iterator))

Question

I'm trying to loop through a fileList in order to perform a delete query. First i fetched data from table "files" in database where attribute "postnumber"=user input. Then it is saved into the "fileList:Files[]". Then a loop through this fileList in order to perform a delete query. but it keeps saying that

"ERROR TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator))". See this image =>

forum-admin-list.component.ts

import { FileService } from 'src/app/shared/file.service';
import { Files } from 'src/app/shared/files.model';
export class ForumAdminListComponent {
fileList:Files[];
onDelete(pNo:string){ 
        this.fservice.getPost(pNo).subscribe(actionArray => {
          this.fileList = actionArray.map(item => {
            return {
              id: item.payload.doc.id,
              ...item.payload.doc.data()
            } as Files;
          })
        });
        for(let i of this.fileList){
          this.storage.storage.refFromURL(i.path).delete();
          this.firestore.doc("files/"+i.id).delete();
        }
  }
}

files.model.ts

export class Files {
    id:string;
    pNo:string;
    downloadURL:string;
    path:string;
}

file.service.ts

export class FileService {
    formData: Files; 
    constructor(private firestore: AngularFirestore) { }

    getPost(userRef){
      return this.firestore.collection('files',ref=>ref.where('pNo','==',userRef)).snapshotChanges();
    }
}

Answer 1

You're looping through the fileList outside the subscribe(), meaning it won't actually wait for the Observable to be resolved. Try to loop inside your subscribe().

onDelete(pNo:string){ 
  this.fservice.getPost(pNo).subscribe(actionArray => {
    this.fileList = actionArray.map(item => {
      return {
        id: item.payload.doc.id,
        ...item.payload.doc.data()
      } as Files[];

      for(let i of this.fileList){
        this.storage.storage.refFromURL(i.path).delete();
        this.firestore.doc("files/"+i.id).delete();
      }
    })
  });
}

Also you might wanna mark the result of the subscription as Files[] instead of as File