RxJS error utils

Utils that help work with errors in rxjs observable's.

Classes

• RxJSFilterError - custom error used by error operators.

Available operators

• filterWithException - works like filter from rxjs, but throw an error instead of ignoring the value.

• rethrowException - will catch any error in the observable, create a new RxJSFilterError (or any custom) with custom message and log it with a custom logger function that you can optionally pass in. If it catches RxJSFilterError (or any custom), it will just rethrow that exception as is.

Usage examples

filterWithException

If the condition does not pass, will throw RxJSFilterError exception with passed in message.

import { of } from 'rxjs';
import { filterWithException } from '@rnw-community/rxjs-errors';

of('C')
    .pipe(
        filterWithException(
            letter => letter === 'A',
            letter => `Wanted A, but got ${letter}`
        )
    )
    .subscribe(value => console.log(value));

Passing custom error class:

import { filterWithException } from '@rnw-community/rxjs-errors';
import { BadRequestException } from '@nestjs/common';
import { of } from 'rxjs';

of('F')
    .pipe(
        filterWithException(
            letter => letter === 'A',
            letter => `Wanted A, but got ${letter}`,
            BadRequestException
        )
    )
    .subscribe(value => console.log(value));

Passing a type guard:

import { filterWithException } from '@rnw-community/rxjs-errors';
import { of } from 'rxjs';

const value: unknown = '';

const isString = (val: unknown): val is string => typeof val === 'string';

of(value) // `unknown` here
    .pipe(filterWithException(isString, value => `Wanted string, but got ${typeof value}`))
    .subscribe((value) /* `string` here */ => {
        console.log(value);
    });

You could also just pass in a message instead of a function:

import { of } from 'rxjs';
import { filterWithException } from '@rnw-community/rxjs-errors';

of('C')
    .pipe(filterWithException(letter => letter === 'A', 'Invalid letter recevied'))
    .subscribe(value => console.log(value));

rethrowException

In this example if the passed in letter is not A, then the RxJSFilterError will be thrown with "Invalid character" text. rethrowException will log it and throw it again as is.

If the this.repository.doSomething(letter) call will throw an error (not an instance of RxJSFilterError) it will log the thrown error, and then create a new one of type RxJSFilterError with "Could not check letter" text.

import { filterWithException, rethrowException } from '@rnw-community/rxjs-errors/src';
import { of } from 'rxjs';

class LetterService {
    constructor(private readonly repository: ILetterRepository) {}

    checkLetter$(letter: string): Observable<string> {
        return of(letter).pipe(
            filterWithException(letter !== 'A', 'Invalid character'),
            concatMap(letter => this.repository.doSomething(letter)),
            rethrowException('Could not check letter', console.error)
        );
    }
}

In this example any error except for LetterError will be caught, logged and a LetterError will be thrown with a "Could not check letter" message.

import { filterWithException, rethrowException } from '@rnw-community/rxjs-errors/src';
import { of } from 'rxjs';

class LetterError extends Error {}

class LetterService {
    constructor(private readonly repository: ILetterRepository) {}

    checkLetter$(letter: string): Observable<string> {
        return of(letter).pipe(
            filterWithException(letter !== 'A', 'Invalid character'),
            concatMap(letter => this.repository.doSomething(letter)),
            rethrowException('Could not check letter', console.error, LetterError)
        );
    }
}

You could also pass in a function, that will accept the caught error, to create an error message:

import { filterWithException, rethrowException } from '@rnw-community/rxjs-errors';
import { getErrorMessage } from '@rnw-community/shared';
import { of } from 'rxjs';

class LetterService {
    constructor(private readonly repository: ILetterRepository) {}

    checkLetter$(letter: string): Observable<string> {
        return of(letter).pipe(
            filterWithException(letter !== 'A', 'Invalid character'),
            concatMap(letter => this.repository.doSomething(letter)),
            rethrowException((err: unknown) => getErrorMessage(err), console.error)
        );
    }
}

If you don't want to log anything, you can just not pass in a log function:

import { filterWithException, rethrowException } from '@rnw-community/rxjs-errors';
import { getErrorMessage } from '@rnw-community/shared';
import { of } from 'rxjs';

class LetterService {
    constructor(private readonly repository: ILetterRepository) {}

    checkLetter$(letter: string): Observable<string> {
        return of(letter).pipe(
            filterWithException(letter !== 'A', 'Invalid character'),
            concatMap(letter => this.repository.doSomething(letter)),
            rethrowException('Could not check letter')
        );
    }
}

License

This library is licensed under The MIT License.