API / rxjs/operators

timeout

Errors if Observable does not emit a value in given time span.

 timeout<T>(due: number | Date, scheduler: SchedulerLike = async): MonoTypeOperatorFunction<T>

Parameters

due

Number specifying period within which Observable must emit values or Date specifying before when Observable should complete
scheduler

Optional. Default is async.

Scheduler controlling when timeout checks occur.

Returns

MonoTypeOperatorFunction<T>: Observable that mirrors behaviour of source, unless timeout checks fail.

Description

Timeouts on Observable that doesn't emit values fast enough.

timeout operator accepts as an argument either a number or a Date.

If number was provided, it returns an Observable that behaves like a source Observable, unless there is a period of time where there is no value emitted. So if you provide 100 as argument and first value comes after 50ms from the moment of subscription, this value will be simply re-emitted by the resulting Observable. If however after that 100ms passes without a second value being emitted, stream will end with an error and source Observable will be unsubscribed. These checks are performed throughout whole lifecycle of Observable - from the moment it was subscribed to, until it completes or errors itself. Thus every value must be emitted within specified period since previous value.

If provided argument was Date, returned Observable behaves differently. It throws if Observable did not complete before provided Date. This means that periods between emission of particular values do not matter in this case. If Observable did not complete before provided Date, source Observable will be unsubscribed. Other than that, resulting stream behaves just as source Observable.

timeout accepts also a Scheduler as a second parameter. It is used to schedule moment (or moments) when returned Observable will check if source stream emitted value or completed.

Examples

Check if ticks are emitted within certain timespan

import { interval } from 'rxjs';
import { timeout } from 'rxjs/operators';

const seconds = interval(1000);

seconds.pipe(timeout(1100))      // Let's use bigger timespan to be safe,
                                 // since `interval` might fire a bit later then scheduled.
.subscribe(
    value => console.log(value), // Will emit numbers just as regular `interval` would.
    err => console.log(err),     // Will never be called.
);

seconds.pipe(timeout(900))
.subscribe(
    value => console.log(value), // Will never be called.
    err => console.log(err),     // Will emit error before even first value is emitted,
                                 // since it did not arrive within 900ms period.
);

Use Date to check if Observable completed

import { interval } from 'rxjs';
import { timeout } from 'rxjs/operators';

const seconds = interval(1000);

seconds.pipe(
  timeout(new Date("December 17, 2020 03:24:00")),
)
.subscribe(
    value => console.log(value), // Will emit values as regular `interval` would
                                 // until December 17, 2020 at 03:24:00.
    err => console.log(err)      // On December 17, 2020 at 03:24:00 it will emit an error,
                                 // since Observable did not complete by then.
);

See Also