startWith
function deprecated operator
Deprecation Notes
The scheduler parameter will be removed in v8. Use scheduled and concatAll. Details: https://rxjs.dev/deprecations/scheduler-argument
startWith<T, A extends readonly, unknown>()
Parameters
There are no parameters.
Overloads
startWith(value: null): OperatorFunction<T, T | null>
Parameters
value |
null |
Returns
OperatorFunction<T, T | null>
startWith(value: undefined): OperatorFunction<T, T | undefined>
Parameters
value |
undefined |
Returns
OperatorFunction<T, T | undefined>
startWith()
Parameters
There are no parameters.
startWith(...values: D[]): OperatorFunction<T, T | D>
Returns an observable that, at the moment of subscription, will synchronously emit all values provided to this operator, then subscribe to the source and mirror all of its emissions to subscribers.
Parameters
values |
D[] |
Items you want the modified Observable to emit first. |
Returns
OperatorFunction<T, T | D>: A function that returns an Observable that synchronously emits provided values before subscribing to the source Observable.
This is a useful way to know when subscription has occurred on an existing observable.
First emits its arguments in order, and then any emissions from the source.
Examples
Emit a value when a timer starts.
import { timer, map, startWith } from 'rxjs';
timer(1000)
.pipe(
map(() => 'timer emit'),
startWith('timer start')
)
.subscribe(x => console.log(x));
// results:
// 'timer start'
// 'timer emit'
© 2015–2022 Google, Inc., Netflix, Inc., Microsoft Corp. and contributors.
Code licensed under an Apache-2.0 License. Documentation licensed under CC BY 4.0.
https://rxjs.dev/api/operators/startWith
