switchMap does not exist on type Observable in Angular

Asked on November 17, 2018
I have an Angular demo project which I have created using Angular 4. Now I updated to Angular 7. But it is not running and throwing error 

"switchmap does not exist on type observable"

How to resolve it?

Replied on November 17, 2018
Angular 6 integrates RxJS 6 and importing RxJS operators has changed.

import { Observable, of } from 'rxjs';
import { mergeMap, switchMap, retry, 
         map, catchError, filter, scan } from 'rxjs/operators';

RxJS operators are used within <code>pipe</code> instance method of Observable.
Find the sample code.

    switchMap(book => {
      let category = book.category;
      return this.bookService.getBooksByCategoryFromStore(category);
    catchError(err => of([]))
  .subscribe(books => {
    this.similarBooks = books;

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