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    RxJS Extra

    Collection of extra RxJS 6 operators, Observable creation methods, Observers and Subjects for common use-cases.

    List of Features


    • cache - Caches the source Observable values for a time period with three different caching strategies.
    • delayComplete - Just like delay() but delays only the complete notification.
    • errorWhen - Emits an error notification when a value matches the predicate function.
    • finalizeWithReason - Just like finalize() but passes to its callback also reason why the chain is being disposed.
    • queueTime - Mirrors the source Observable and makes at most timeDelay delay between two emissions to keep at least timeDelay intervals while re-emitting source asap.
    • randomDelay - Mirrors the source Observable but makes random delays between emissions on a specified scheduler.
    • retryTime - Just like retry() but resubscribes to its source Observable with constant delays or resubscribes only N times based on a predefined array of delays.
    • takeUntilComplete - Just like takeUntil() but completes only when the notifier completes and ignores all next notifications.
    • tapSubscribe - Triggers callback every time a new observer subscribes to this chain.

    Observable creation methods

    • presetTimer - Creates an Observable that emits sequential numbers in predefined delays on a specified scheduler.
    • randomTimer - Creates an Observable that emits sequential numbers in random intervals on a specified scheduler.


    • DebugObserver - Observer for debugging purposes that timestamps each notification with time offset since the instance was created.


    • PersistentSubject - Just like BehaviorSubject but stores every item in a persistent storage (LocalStorage by default).


    Install rxjs-extra via npm:

    npm install rxjs-extra

    The general usage is the same as with any RxJS 6 operators or Observable creation methods:

    In TypeScript for example:

    import { map } from 'rxjs/operators';
    import { randomTimer } from 'rxjs-extra';
    import { tapSubscribe } from 'rxjs-extra/operators';
    randomTimer(100, 2000).pipe(
      tapSubscribe(() => console.log('subscribed')),
      map(i => String.fromCharCode(97 + i)),

    In node environment for example:

    const { map } = require('rxjs/operators');
    const { randomTimer } = require('rxjs-extra');
    const { tapSubscribe } = require('rxjs-extra/operators');
    randomTimer(100, 2000).pipe(
      tapSubscribe(() => console.log('subscribed')),
      map(i => String.fromCharCode(97 + i)),


    All features from this package have their small demo examples written in TypeScript. You can use NPM demo script with preconfigures ts-node to run any one of them:

    $ npm run demo -- demo/delayComplete.ts


    This repository tests are based completely on RxJS marble tests and its helpers. You'll have to clone the original RxJS repo because tests in this repo rely on tools available only in the official RxJS 6 repo.

    $ npm run clone_rxjs_repo

    To run the test suit simply run the following npm script:

    $ npm run test

    This repository also uses the same marble2png generator as the original RxJS repo. Since this isn't an officially exported feature of RxJS 6 the process is a little more complicated but fully automatic by running a single script:

    $ npm run tests2png_full

    The tests2png_full script does the following things:

    1. Clones repo into .rxjs-repo directory.

    2. Creates ./docs_app/content/img/ directory.

    3. Runs mocha tests with tests2png.opts options.

    4. Copies content of ./docs_app/content/img/ to ./doc.

    5. Removes temp directories .rxjs-repo and ./docs_app.

    If you know you're about to run the png generator a lot you can just clone the RxJS repo and re-run the test suit:

    $ npm run clone_rxjs_repo
    $ npm run tests2png


    npm i rxjs-extra

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    • martinsik