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import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { Observable } from '../Observable';
import { OperatorFunction } from '../types';
/**
* Emits the given constant value on the output Observable every time the source
* Observable emits a value.
*
* <span class="informal">Like {@link map}, but it maps every source value to
* the same output value every time.</span>
*
* 
*
* 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'
* ```javascript
* 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 {@link map}
*
* @param {any} value The value to map each source value to.
* @return {Observable} An Observable that emits the given `value` every time
* the source Observable emits something.
* @method mapTo
* @owner Observable
*/
export function mapTo<T, R>(value: R): OperatorFunction<T, R> {
return (source: Observable<T>) => source.lift(new MapToOperator(value));
}
class MapToOperator<T, R> implements Operator<T, R> {
value: R;
constructor(value: R) {
this.value = value;
}
call(subscriber: Subscriber<R>, source: any): any {
return source.subscribe(new MapToSubscriber(subscriber, this.value));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class MapToSubscriber<T, R> extends Subscriber<T> {
value: R;
constructor(destination: Subscriber<R>, value: R) {
super(destination);
this.value = value;
}
protected _next(x: T) {
this.destination.next(this.value);
}
}
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