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node_modules/rxjs/src/internal/observable/interval.ts

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+import { Observable } from '../Observable';
+import { asyncScheduler } from '../scheduler/async';
+import { SchedulerLike } from '../types';
+import { timer } from './timer';
+
+/**
+ * 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.png)
+ *
+ * `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
+ *
+ * ```ts
+ * import { interval, take } from 'rxjs';
+ *
+ * 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 period The interval size in milliseconds (by default) or the time unit determined
+ * by the scheduler's clock.
+ * @param scheduler The {@link SchedulerLike} to use for scheduling the emission of values,
+ * and providing a notion of "time".
+ * @return An Observable that emits a sequential number each time interval.
+ */
+export function interval(period = 0, scheduler: SchedulerLike = asyncScheduler): Observable<number> {
+  if (period < 0) {
+    // We cannot schedule an interval in the past.
+    period = 0;
+  }
+
+  return timer(period, period, scheduler);
+}