timer

A delay before the first value, plus an optional interval.

Signature

timer(initialDelay: number | Date, period?: number): Observable

Marble diagram

timer(20):    --(0|)
timer(20, 10):  --0--1--2-- ...

What it does

Waits initialDelay (in ms or a Date), emits 0, and completes. If period is given, it continues like interval(period), emitting 1, 2, 3… Unlike interval, the first value arrives exactly after initialDelay, which can be zero.

When to use

A deferred task start, emulating a debounce, retry with backoff (retry({ delay: i => timer(2 ** i * 100) })), timeouts, an artificial delay for UI effects.

See also

interval, delay, retry