import { OperatorFunction } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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export function map<T, R>(project: (value: T, index: number) => R): OperatorFunction<T, R>;
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/** @deprecated Use a closure instead of a `thisArg`. Signatures accepting a `thisArg` will be removed in v8. */
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export function map<T, R, A>(project: (this: A, value: T, index: number) => R, thisArg: A): OperatorFunction<T, R>;
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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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*
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* Map every click to the `clientX` position of that click
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*
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* ```ts
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* import { fromEvent, map } from 'rxjs';
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*
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* const clicks = fromEvent<PointerEvent>(document, 'click');
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* const positions = clicks.pipe(map(ev => ev.clientX));
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*
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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 A function that returns an Observable that emits the values from the
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* source Observable transformed by the given `project` function.
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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 operate((source, subscriber) => {
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// The index of the value from the source. Used with projection.
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let index = 0;
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// Subscribe to the source, all errors and completions are sent along
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// to the consumer.
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source.subscribe(
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createOperatorSubscriber(subscriber, (value: T) => {
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// Call the projection function with the appropriate this context,
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// and send the resulting value to the consumer.
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subscriber.next(project.call(thisArg, value, index++));
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})
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);
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});
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}
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