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import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { Observable } from '../Observable';
import { OperatorFunction } from '../types';
/**
* Applies a given `project` function to each value emitted by the source
* Observable, and emits the resulting values as an Observable.
*
* <span class="informal">Like [Array.prototype.map()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map),
* it passes each source value through a transformation function to get
* corresponding output values.</span>
*
* ![](map.png)
*
* Similar to the well known `Array.prototype.map` function, this operator
* applies a projection to each value and emits that projection in the output
* Observable.
*
* ## Example
* Map every click to the clientX position of that click
* ```ts
* import { fromEvent } from 'rxjs';
* import { map } from 'rxjs/operators';
*
* const clicks = fromEvent(document, 'click');
* const positions = clicks.pipe(map(ev => ev.clientX));
* positions.subscribe(x => console.log(x));
* ```
*
* @see {@link mapTo}
* @see {@link pluck}
*
* @param {function(value: T, index: number): R} project The function to apply
* to each `value` emitted by the source Observable. The `index` parameter is
* the number `i` for the i-th emission that has happened since the
* subscription, starting from the number `0`.
* @param {any} [thisArg] An optional argument to define what `this` is in the
* `project` function.
* @return {Observable<R>} An Observable that emits the values from the source
* Observable transformed by the given `project` function.
* @method map
* @owner Observable
*/
export function map<T, R>(project: (value: T, index: number) => R, thisArg?: any): OperatorFunction<T, R> {
return function mapOperation(source: Observable<T>): Observable<R> {
if (typeof project !== 'function') {
throw new TypeError('argument is not a function. Are you looking for `mapTo()`?');
}
return source.lift(new MapOperator(project, thisArg));
};
}
export class MapOperator<T, R> implements Operator<T, R> {
constructor(private project: (value: T, index: number) => R, private thisArg: any) {
}
call(subscriber: Subscriber<R>, source: any): any {
return source.subscribe(new MapSubscriber(subscriber, this.project, this.thisArg));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class MapSubscriber<T, R> extends Subscriber<T> {
count: number = 0;
private thisArg: any;
constructor(destination: Subscriber<R>,
private project: (value: T, index: number) => R,
thisArg: any) {
super(destination);
this.thisArg = thisArg || this;
}
// NOTE: This looks unoptimized, but it's actually purposefully NOT
// using try/catch optimizations.
protected _next(value: T) {
let result: any;
try {
result = this.project.call(this.thisArg, value, this.count++);
} catch (err) {
this.destination.error(err);
return;
}
this.destination.next(result);
}
}
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