属性“ of”在类型“ typeof Observable”上不存在。ts（2339）

Question

import { Injectable } from '@angular/core';
import { Book } from './book';
import { Observable } from 'rxjs';
import { of } from 'rxjs';




@Injectable({
  providedIn: 'root'
})
export class BookService {

  constructor() { }


  BOOKS : Book[]=[
    
    {"id": 1, "name" : "JavaScript",  "price" :"100", "description": "javscript"},
    {"id": 2, "name" : "Angualr",  "price" :"200", "description": "Angualr"},
    {"id": 3, "name" : "Sql server",  "price" :"3000", "description": "Sql server"},
    {"id": 4, "name" : "Typescript",  "price" :"5000", "description": "Typescript"},
    
  ]


  getBooks(): Observable<Book[]>{
    return Observable.of(this.BOOKS);
  }
}

类型为“可观察的类型”的属性不存在“ of”。ts（2339）

我尝试了两个import语句，仍然给出了

import { of } from 'rxjs';
import 'rxjs/add/observable/of';

类型为'typeof Observable'的属性'of'不存在.ts（2339） 属性“ of”在类型“ typeof Observable”上不存在。ts（2339） 属性“ of”在类型“ typeof Observable”上不存在。ts（2339）