Unable to get the value of a Promise . Error “Property ‘Choices’ does not exist on type ‘Promise'” [duplicate]

I have the following type script inside my ReactJs SPFx sharepoint online web part:-

import * as React from 'react';
import * as ReactDom from 'react-dom';
import { Version } from '@microsoft/sp-core-library';
import {
  IPropertyPaneConfiguration,
  IPropertyPaneDropdownOption,
  PropertyPaneDropdown} from '@microsoft/sp-property-pane';
import { BaseClientSideWebPart } from '@microsoft/sp-webpart-base';

import * as strings from 'ContactListWebPartStrings';
import ContactListApp from './components/ContactListApp';
import { IContactListProps } from './components/IContactListProps';
import { sp } from "@pnp/sp/presets/all";


export interface IContactListWebPartProps {
  department: string;
}

export default class ContactListWebPart extends BaseClientSideWebPart<IContactListWebPartProps> {
  private viewModeOptions: IPropertyPaneDropdownOption[] = null;
  public render(): void {
    const element: React.ReactElement<IContactListProps> = React.createElement(
      ContactListApp,
      {
        department: this.properties.department,
        context: this.context
      }
    );

    ReactDom.render(element, this.domElement);
  }

  protected onDispose(): void {
    ReactDom.unmountComponentAtNode(this.domElement);
  }

  protected get dataVersion(): Version {
    return Version.parse('1.0');
  }
  public onInit(): Promise<void> {
    return super.onInit().then( _ => {
      sp.setup({
        spfxContext: this.context
      });
      const choice =  
      sp.web.lists.getByTitle('Contacts').fields.getByTitle('Department').get();
      this.viewModeOptions = choice.Choices.map((choice: string, idx: number) => 
      {
        return {
         key: idx,
         text: choice
        }
      })
   });
  }


  protected getPropertyPaneConfiguration(): IPropertyPaneConfiguration {
    return {
      pages: [
        {
          header: {
            description: strings.PropertyPaneDescription
          },
          groups: [
            {
              groupName: strings.BasicGroupName,
              groupFields: [
                PropertyPaneDropdown('department', {
                  label: 'Department',
                  options: this.viewModeOptions,
                  selectedKey: this.viewModeOptions[0].key,
                  disabled: !this.viewModeOptions
                 }),
              ]
            }
          ]
        }
      ]
    };
  }
}

but i am getting this error on choice.Choices.map:-

Property ‘Choices’ does not exist on type ‘Promise’

here is my web part details:-

{
  "@microsoft/generator-sharepoint": {
    "isCreatingSolution": true,
    "environment": "spo",
    "version": "1.12.1",
    "libraryName": "contact-list-webpart",
    "libraryId": "aa3dbbd0-0d6b-4cae-98b0-c29c37998c6e",
    "packageManager": "npm",
    "isDomainIsolated": false,
    "componentType": "webpart"
  }
}