Reference · 35

tap

A side effect that doesn't change the value.

Signature

tap(observerOrNext?: Partial> | ((value: T) => void)): MonoTypeOperatorFunction

Marble diagram

in:    --1--2--|
result: --1--2--|  (callback fired on each)

What it does

Calls a function for each next/error/complete; the stream passes through unchanged. You can pass either a single function (next only) or a full observer object.

When to use

Logging while debugging, updating UI flags (loading), recording analytics, dev-inspecting values in the middle of a pipe. Better than map for anything that doesn't return a new value.

Gotcha

tap is the place for side effects, but not for all of them. Don't modify the value "on the sly" (by mutating an object) — that surprises the subscriber.

tap

tap

Signature

Marble diagram

What it does

When to use

See also