API / rxjs/operators

mapTo

Emits the given constant value on the output Observable every time the source Observable emits a value.

mapTo<T, R>(value: R): OperatorFunction<T, R>

Parameters

value

The value to map each source value to.

Returns

OperatorFunction<T, R>: An Observable that emits the given value every time the source Observable emits something.

Description

Like map, but it maps every source value to the same output value every time.

Takes a constant value as argument, and emits that whenever the source Observable emits a value. In other words, ignores the actual source value, and simply uses the emission moment to know when to emit the given value.

Example

Map every click to the string 'Hi'

import { fromEvent } from 'rxjs'; import { mapTo } from 'rxjs/operators'; const clicks = fromEvent(document, 'click'); const greetings = clicks.pipe(mapTo('Hi')); greetings.subscribe(x => console.log(x));

See Also