mapTo

function stable

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

`mapTo<R>(value: R): OperatorFunction<any, R>`

Parameters

value

The value to map each source value to.

Returns

OperatorFunction<any, R>: A function that returns an Observable that emits the given value every time the source Observable emits.

Description

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

mapTo marble diagram

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));