pouchDb中的呼叫提供者服务给出＆＃34; TypeError：无法设置属性＆＃39; itemsList＆＃39;未定义＆＃34;

Question

在pouchdb回调中调用CommonServiceProvider时，不会给出联系人详细信息，而是提供错误：

  

错误错误：未捕获（在承诺中）：TypeError：无法设置属性＆＃39; itemsList＆＃39;未定义的   TypeError：无法设置属性＆＃39; itemsList＆＃39;未定义的

import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import PouchDB from 'pouchdb';
import { CommonServiceProvider } from '../../providers/common-service/common-service';

@IonicPage()
@Component({
  selector: 'page-contact-lists',
  templateUrl: 'contact-lists.html',
})
export class ContactListsPage {
  public itemsList;
  searchQuery: string = '';
  private db;
  constructor(private commonServiceProvider: CommonServiceProvider, public navCtrl: NavController, public navParams: NavParams) { }
  setupDB() {
    this.db = new PouchDB('Contacts');
  }

  ionViewDidLoad() {
    this.setupDB();  //DB Setup
    // Function to check if doc is exixts in DB or not
    this.db.allDocs({
      include_docs: true,
      attachments: true
    }, function (err, response) {
      if (!err) {
        //if DB don't have any doc, call the contact service to fatch data
        if (response.total_rows == 0) {
          this.commonServiceProvider.fetchContacts()
            .subscribe((data: any) => {
              if (data.responseCode === 0) {
                this.itemsList = data.contacts;
                // Insert service data in DB
                this.db.bulkDocs(data.contacts, (err, result) => {
                  if (!err) {
                  }else{
                    console.log(err);
                  }
                });
              } else { }
            }, err => {
              console.log(err);
            });
        } else {
          this.itemsList = response.rows;
        }
      } else {
        console.log(err);
      }
    });
  }
}