ReactiveX/rxjs · error · Error

Scheduler-backed generate is not supported by this Symbol co

Error message

Scheduler-backed generate is not supported by this Symbol contract.

What it means

generate() in RxJS Next has no scheduler support. When called with a single options object, presence of a 'scheduler' property with a non-undefined value throws, because scheduler-backed timing is outside the Symbol contract.

Source

Thrown at packages/rxjs/src/generate.ts:43

  }
}

Observable[generate] = function generateImpl<T, S>(
  this: ObservableCtor,
  initialStateOrOptions: S | GenerateOptions<T, S>,
  condition?: (state: S) => boolean,
  iterate?: (state: S) => S,
  resultSelector?: (state: S) => T
): Observable<T | S> {
  let initialState: S;
  let selectedCondition: ((state: S) => boolean) | undefined;
  let selectedIterate: (state: S) => S;
  let selectedResult: (state: S) => T | S;

  if (arguments.length === 1) {
    const options = initialStateOrOptions as GenerateOptions<T, S>;
    if ('scheduler' in (options as object) && (options as GenerateOptions<T, S> & { scheduler?: unknown }).scheduler !== undefined) {
      throw new Error('Scheduler-backed generate is not supported by this Symbol contract.');
    }
    initialState = options.initialState;
    selectedCondition = options.condition;
    selectedIterate = options.iterate;
    selectedResult = options.resultSelector ?? ((state) => state);
  } else {
    if (arguments.length > 4) {
      throw new Error('Scheduler-backed generate is not supported by this Symbol contract.');
    }
    initialState = initialStateOrOptions as S;
    selectedCondition = condition;
    selectedIterate = iterate as (state: S) => S;
    selectedResult = resultSelector ?? ((state) => state);
  }

  return this[create]((subscriber) => {
    let state = initialState;

View on GitHub (pinned to 54796b38a5)

Solutions

1. Delete the scheduler property from the options object
2. Apply scheduling after generation: generate({...}).pipe(observeOn-like operator) or in the testing layer use the TestScheduler marble harness

Example fix

// before
generate({ initialState: 0, iterate: s => s + 1, scheduler: asyncScheduler });
// after
generate({ initialState: 0, iterate: s => s + 1 });

const { scheduler: _ignored, ...opts } = options; // strip legacy key
obs ?? generate(opts);

const hasScheduler = (o: object) => 'scheduler' in o && (o as any).scheduler !== undefined;

When it happens

Trigger: generate({ initialState: 0, condition: s => s < 5, iterate: s => s + 1, scheduler: asyncScheduler }).

Common situations: RxJS 7 code that used generate with a scheduler (common in tests and polling) running unchanged against RxJS Next, or copy-pasted options including scheduler: null from docs.

Related errors

• RxJS Next expand does not support a scheduler argument.
• Scheduler-backed publishReplay is not supported by this Symb
• Scheduler-backed shareReplay is not supported by this Symbol
• A combineLatest projection requires an array of observable v
• RxJS Next expand options must be an object.

AI-assisted analysis of ReactiveX/rxjs@54796b38a5 (2026-08-28). Data as JSON: /api/errors/c7a4d55f7c1525fd. Report an issue: GitHub.