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