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import { Observable } from '../Observable';
import { async } from '../scheduler/async';
import { SchedulerAction, SchedulerLike } from '../types';
import { isNumeric } from '../util/isNumeric';
import { Subscriber } from '../Subscriber';
/**
* Creates an Observable that emits sequential numbers every specified
* interval of time, on a specified {@link SchedulerLike}.
*
* <span class="informal">Emits incremental numbers periodically in time.
* </span>
*
* 
*
* `interval` returns an Observable that emits an infinite sequence of
* ascending integers, with a constant interval of time of your choosing
* between those emissions. The first emission is not sent immediately, but
* only after the first period has passed. By default, this operator uses the
* `async` {@link SchedulerLike} to provide a notion of time, but you may pass any
* {@link SchedulerLike} to it.
*
* ## Example
* Emits ascending numbers, one every second (1000ms) up to the number 3
* ```javascript
* import { interval } from 'rxjs';
* import { take } from 'rxjs/operators';
*
* const numbers = interval(1000);
*
* const takeFourNumbers = numbers.pipe(take(4));
*
* takeFourNumbers.subscribe(x => console.log('Next: ', x));
*
* // Logs:
* // Next: 0
* // Next: 1
* // Next: 2
* // Next: 3
* ```
*
* @see {@link timer}
* @see {@link delay}
*
* @param {number} [period=0] The interval size in milliseconds (by default)
* or the time unit determined by the scheduler's clock.
* @param {SchedulerLike} [scheduler=async] The {@link SchedulerLike} to use for scheduling
* the emission of values, and providing a notion of "time".
* @return {Observable} An Observable that emits a sequential number each time
* interval.
* @static true
* @name interval
* @owner Observable
*/
export function interval(period = 0,
scheduler: SchedulerLike = async): Observable<number> {
if (!isNumeric(period) || period < 0) {
period = 0;
}
if (!scheduler || typeof scheduler.schedule !== 'function') {
scheduler = async;
}
return new Observable<number>(subscriber => {
subscriber.add(
scheduler.schedule(dispatch, period, { subscriber, counter: 0, period })
);
return subscriber;
});
}
function dispatch(this: SchedulerAction<IntervalState>, state: IntervalState) {
const { subscriber, counter, period } = state;
subscriber.next(counter);
this.schedule({ subscriber, counter: counter + 1, period }, period);
}
interface IntervalState {
subscriber: Subscriber<number>;
counter: number;
period: number;
}
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