Angular 6 RXJS Import Syntax?

Question

I'm migrating an Angular 5 app to the latest CLI and Angular 6 RC and all of my Observable imports are broken. I see that Angular 6 changes the way the imports work, but I can't find any definite reference as to how the syntax works.

I had this in 5 and it worked fine:

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';

Now with the new syntax I see that

import { Observable, Subject, throwError} from 'rxjs';
import { map } from 'rxjs/operators';

The first two lines compile, but I can't figure out how to get catch and throw for example. .map() also throws a build error when used in code.

Anybody have a reference to how this is supposed to work?

Answer 1

From rxjs 5.5, catch has been renamed to catchError function to avoid name clash.

Due to having operators available independent of an Observable, operator names cannot conflict with JavaScript keyword restrictions. Therefore the names of the pipeable version of some operators have changed.

import { catchError } from 'rxjs/operators';

For throw you can use ErrorObservable.

import { ErrorObservable } from 'rxjs/observable/ErrorObservable';
ErrorObservable.create(new Error("oops"));

rxjs 6

Instead of ErrorObservable use throwError.

 import { throwError } from 'rxjs'
 throwError(new Error("oops"));

Also you will now have to pipe the operators instead of directly chaining them to the observable

Answer 2

Pipes are what is required for operator(s) going forward.

version: rxjs 6.0.1

Example:

import { Observable } from "rxjs";
import { map } from "rxjs/operators";

Observable.create((observer: any) => {
    observer.next('Hello')
}).pipe(map((val: any) => val.toUpperCase()))
  .subscribe((x: any) => addItem(x))


function addItem(val: any) {
    console.log('val', val);
}

//output - (In uppercase)
HELLO

Answer 3

Run these 2 commands after running ng update. This should fix the rxjs imports:

1. npm i -g rxjs-tslint
2. rxjs-5-to-6-migrate -p src/tsconfig.app.json

References:

• https://github.com/ReactiveX/rxjs-tslint