“rxjs” observable.throw is not a function - Angular4

Question

I've been learning Angular 4 and everything was going smoothly until I tried to implement catch handling in a service. I'm trying to use "rxjs" catch and throw but I've got an undefined function error in my console.

import { Injectable } from '@angular/core';
import { Http } from "@angular/http";
import { Observable } from 'rxjs/observable';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';
import { AppError } from "../app/common/app.error";
import { NotFoundError } from "../app/common/not-found-error";
import { BadInput } from "../app/common/bad-input";

@Injectable()
export class PostService {
  private url = "https://jsonplaceholder.typicode.com/posts";

  constructor(private http: Http) { }

 deletepost(post){
      // return this.http.delete(this.url + '/' + post.id)
      // Hard-coded id to test 404
      return this.http.delete(this.url + '/' + 93498)
        .catch((error: Response) => {
          console.log('error within catch is ' + Response)
          if(error.status === 404)
            return Observable.throw(new NotFoundError(error));

          return Observable.throw(new AppError(error));
        });
    }
}

This is the error message:

TypeError: __WEBPACK_IMPORTED_MODULE_2_rxjs_observable__["Observable"].throw is not a function. 
(In '__WEBPACK_IMPORTED_MODULE_2_rxjs_observable__["Observable"].throw(new 
__WEBPACK_IMPORTED_MODULE_6__app_common_not_found_error__["a" /* NotFoundError 
*/](error))', 
'__WEBPACK_IMPORTED_MODULE_2_rxjs_observable__["Observable"].throw' is 
undefined) — post.service.ts:42

I also have this warning in my browser:

./~/rxjs/Observable.js
There are multiple modules with names that only differ in casing.
This can lead to unexpected behavior when compiling on a filesystem with other case-semantic.
Use equal casing. Compare these module identifiers:
* /Users/nickgowdy/Desktop/Angular2/angular4 source code/hello-world/node_modules/rxjs/Observable.js
    Used by 14 module(s), i. e.
    /Users/nickgowdy/Desktop/Angular2/angular4 source code/hello-world/node_modules/@angular/core/@angular/core.es5.js
* /Users/nickgowdy/Desktop/Angular2/angular4 source code/hello-world/node_modules/rxjs/observable.js
    Used by 1 module(s), i. e.
    /Users/nickgowdy/Desktop/Angular2/angular4 source code/hello-world/node_modules/@ngtools/webpack/src/index.js!/Users/nickgowdy/Desktop/Angular2/angular4 source code/hello-world/src/services/post.service.ts

Answer 1

The error There are multiple modules with names that only differ in casing. is indicating the wrong import is being targeted with how you are trying to use Observable .

The import should be with a capital "O" like:

import { Observable } from 'rxjs/Observable';

This will import the individual Observable operator, which be used in combination with operators such as catch or throw on created Observables.

import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

To import the full Observable object you'd import it like this:

import { Observable } from 'rxjs/Rx'

Update:

With newer versions of RxJS (5.5+) operators such as map() and filter() can used as pipeable operators in combination with pipe() rather than chaining. They are imported such as:

import { filter, map, catchError } from 'rxjs/operators';

Keep in mind terms such as throw are reserved/key words in JavaScript so the RxJS throw operator is imported as:

import { _throw } from 'rxjs/observable/throw';

Update:

For newer versions of RxJS (6+), use this:

import { throwError } from 'rxjs';

and throw an error like this:

if (error.status === 404)
    return throwError( new NotFoundError(error) )

Answer 2

In RxJS 6, Observable.throw() is replaced by throwError() which operates very similarly to its predecessor. So, you can replace from Observable.throw(error) to only throwError(error) by importing:

import { throwError } from 'rxjs';

Checkout this link for further reference: https://www.metaltoad.com/blog/angular-6-upgrading-api-calls-rxjs-6

Answer 3

I was facing the same issue in my angular 5 application. What I did is, adding a new package.

import { throwError } from 'rxjs';
import { filter, map, catchError } from 'rxjs/operators';

And from my http service call I return a function.

return this.http.request(request)
      .pipe(map((res: Response) => res.json()),
        catchError((res: Response) => this.onError(res)));

And in onError function I am returning the error with throwError(error) .

onError(res: Response) {
    const statusCode = res.status;
    const body = res.json();
    const error = {
      statusCode: statusCode,
      error: body.error
    };
    return throwError(error);
  }

Answer 4

_throw has been discarded in newer versions of RxJS
For newer versions of RxJS (6+), use this:

import { throwError } from 'rxjs';

and throw an error like this:

if (error.status === 404)
    return throwError( new NotFoundError(error) )

Answer 5

In Angular9 Observable:

1. if data arrived and status is OK, then send the data
2. If STATUS of the data is NOT OK, then throw an error

myObsFunc(): Observable<any> { 
  return this.http.get<any>('/api/something') 
    .pipe(
      /* Catch a backend error and let the component know */
      catchError( err => {
        /* Rethrow error */
        return throwError( err );
      }),
      map( (res)=> {
        if( res.STATUS == "OK" ) {
          /* Send DATA to subscriber */
          return Object.values( res.DATA)
        } else {
           /* Inform subscriber that a functional error occured */
           throw ( "getOrphans: Status is not OK but "+ res.STATUS ) ;
        }   
      }),
    )   
}